Vehicle height adjustment device

ABSTRACT

A vehicle height adjustment device includes a changer, a vehicle speed obtainer, a vehicle height controller, and a malfunction detector. The changer is configured to change a relative position of a body of a vehicle, which includes a plurality of wheels, relative to an axle of each of the plurality of wheels of the vehicle. The vehicle speed obtainer is configured to obtain a vehicle speed, which is a traveling speed of the vehicle. The vehicle height controller is configured to control a vehicle height, which is a height of the body, based on the vehicle speed obtained by the vehicle speed obtainer. The malfunction detector is configured to detect a failure of the vehicle speed obtainer to obtain an accurate value of the vehicle speed.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. §119 to JapanesePatent Application No. 2016-054512, filed Mar. 17, 2016. The contents ofthis application are incorporated herein by reference in their entirety.

BACKGROUND

Field

The present disclosure relates to a vehicle height adjustment device.

Related Art

Japanese Examined Patent Publication No. H08-22680 discloses a vehicleheight adjustment device that increases the height of a motorcycleduring travel and that decreases the height of the motorcycle duringhalt in order to facilitate a rider's or a passenger's getting on andoff the motorcycle.

The vehicle height adjustment device automatically changes the height ofthe motorcycle in response to its speed of travel. Specifically, thevehicle height adjustment device automatically increases the height ofthe motorcycle when its speed reaches a set speed, and automaticallydecreases the height of the motorcycle when its speed changes to orbelow a set speed. In the adjustment of the height of the motorcycle, anelectromagnetic actuator is driven into operation.

SUMMARY

According to one aspect of the present disclosure, a vehicle heightadjustment device includes a changer, a vehicle speed obtainer, avehicle height controller, and a malfunction detector. The changer isconfigured to change a relative position of a body of a vehicle, whichincludes a plurality of wheels, relative to an axle of each of theplurality of wheels of the vehicle. The vehicle speed obtainer isconfigured to obtain a vehicle speed, which is a traveling speed of thevehicle. The vehicle height controller is configured to control avehicle height, which is a height of the body, based on the vehiclespeed obtained by the vehicle speed obtainer. The malfunction detectoris configured to detect a failure of the vehicle speed obtainer toobtain an accurate value of the vehicle speed.

According to another aspect of the present disclosure, a vehicle heightadjustment device includes a changer and a vehicle height controller.The changer is configured to change a position of a body of a vehiclerelative to an axle of a wheel of the vehicle. When a vehicle speed,which is a traveling speed of the vehicle, is equal to or higher than apredetermined upward speed, the vehicle height controller is configuredto control the changer to make the relative position a target relativeposition. When a difference between the actual relative position and thetarget relative position starts to increase although the vehicle speedis equal to or higher than the upward speed, and after a predeterminedperiod of time elapses after the difference starts to increase, thevehicle height controller is configured to control the changer to makethe relative position the target relative position before the differencestarts to increase.

According to the other aspect of the present disclosure, a vehicleheight adjustment device includes a changer and a vehicle heightcontroller. The changer is configured to change a position of a body ofa vehicle relative to an axle of a wheel of the vehicle. When a vehiclespeed, which is a traveling speed of the vehicle, is equal to or higherthan a predetermined upward speed, the vehicle height controller isconfigured to control the changer to make the relative position a targetrelative position. When a difference between the actual relativeposition and the target relative position starts to increase althoughthe vehicle speed is equal to or higher than the upward speed, and aftera predetermined period of time elapses after the difference starts toincrease, the vehicle height controller is configured to control thechanger to maintain a vehicle height, which is a height of the body.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the present disclosure and many of theattendant advantages thereof will be readily obtained as the samebecomes better understood by reference to the following detaileddescription when considered in connection with the accompanyingdrawings, wherein:

FIG. 1 illustrates a schematic configuration of a motorcycle accordingto an embodiment;

FIG. 2 is a cross-sectional view of a front fork according to theembodiment;

FIG. 3 is an enlarged view of part III illustrated in FIG. 2;

FIG. 4 is an enlarged view of part IV illustrated in FIG. 3;

FIG. 5 illustrates how the front fork operates at a time of acompression stroke;

FIG. 6 illustrates how the front fork operates at a time of a reboundstroke;

FIG. 7 illustrates a flow of oil in a front-wheel passage switch unit ina first switch state;

FIG. 8 illustrates a flow of the oil in the front-wheel passage switchunit in a second switch state;

FIG. 9 illustrates a flow of the oil in the front-wheel passage switchunit in a third switch state;

FIG. 10 illustrates a flow of the oil in the front-wheel passage switchunit in a fourth switch state;

FIG. 11A illustrates whether a first communication passage, a secondcommunication passage, and a third communication passage are open orclosed when the front-wheel passage switch unit is in the first switchstate;

FIG. 11B illustrates whether the first communication passage, the secondcommunication passage, and the third communication passage are open orclosed when the front-wheel passage switch unit is in the second switchstate;

FIG. 11C illustrates whether the first communication passage, the secondcommunication passage, and the third communication passage are open orclosed when the front-wheel passage switch unit is in the third switchstate;

FIG. 12 is a block diagram of a controller;

FIG. 13 is a block diagram of a passage switch unit controller;

FIG. 14A is a time chart illustrating malfunction when a failure toobtain an accurate vehicle speed Vv occurs;

FIG. 14B is a time chart illustrating control details of a malfunctiondetector according to the embodiment;

FIG. 15 is a flowchart of a procedure for control processing performedby the malfunction detector; and

FIG. 16 is a time chart illustrating other control details of themalfunction detector according to the embodiment.

DESCRIPTION OF THE EMBODIMENTS

The embodiments will now be described with reference to the accompanyingdrawings, wherein like reference numerals designate corresponding oridentical elements throughout the various drawings.

FIG. 1 illustrates a schematic configuration of a motorcycle 1 accordingto this embodiment.

The motorcycle 1 includes a front wheel 2, a rear wheel 3, and a body10. The front wheel 2 is a wheel on the front side of the motorcycle 1.The rear wheel 3 is a wheel on the rear side of the motorcycle 1. Thebody 10 includes elements such as a frame 11, a handle 12, an engine 13,and a seat 19. The frame 11 defines the framework of the motorcycle 1.

The motorcycle 1 includes two front forks 21. One of the front forks 21is on the right side of the front wheel 2, and the other one of thefront forks 21 is on the left side of the front wheel 2. The front forks21 are examples of a suspension device that couples the front wheel 2and the body 10 to each other. The motorcycle 1 includes two rearsuspensions 22. One of the rear suspensions 22 is on the right side ofthe rear wheel 3, and the other one of the rear suspensions 22 is on theleft side of the rear wheel 3. The rear suspensions 22 couple the rearwheel 3 and the body 10 to each other. FIG. 1 illustrates only the frontfork 21 and the rear suspension 22 that are on the right side of themotorcycle 1. The front fork 21 and the rear suspension 22 are anexample of the changer to change a relative position of the body 10relative to the axle of the front wheel 2 and a relative position of thebody 10 relative to the axle of the rear wheel 3.

The motorcycle 1 includes two brackets 14 and a shaft 15. The shaft 15is disposed between the two brackets 14. The two brackets 14respectively hold the front fork 21 on a right side of the front wheel 2and the front fork 21 on a left side of the front wheel 2. The shaft 15is rotatably supported by the frame 11.

The motorcycle 1 includes a controller 70. The controller 70 controls aheight of the motorcycle 1 by controlling a front-wheel passage switchunit 300, described later, of each front fork 21 and a rear-wheelpassage switch unit 302, described later, of each rear suspension 22.

The motorcycle 1 also includes a front-wheel rotation detection sensor31 and a rear-wheel rotation detection sensor 32. The front-wheelrotation detection sensor 31 detects a rotation angle of the front wheel2. The rear-wheel rotation detection sensor 32 detects a rotation angleof the rear wheel 3.

It is noted that the front-wheel rotation detection sensor 31 and therear-wheel rotation detection sensor 32 are examples of the rotationangle detectors to detect rotation angles of a plurality of wheels. Therotation angle detectors are disposed on the respective wheels. Thefront-wheel rotation detection sensor 31 is an example of the firstrotation angle detector, and the rear-wheel rotation detection sensor 32is an example of the second rotation angle detector.

Each front fork 21 will be described in detail below.

FIG. 2 is a cross-sectional view of the front fork 21 according to thisembodiment.

The front fork 21 according to this embodiment is what is called anupright front fork that is disposed between the body 10 and the frontwheel 2 of the motorcycle 1 so as to support the front wheel 2. Theupright front fork 21 includes an outer member 110 (detailed later) andan inner tube 210 (detailed later). The outer member 110 is disposed onthe side of the front wheel 2, and the inner tube 210 is disposed on theside of the body 10.

The front fork 21 includes an axle side unit 100 and a body side unit200. The axle side unit 100 includes the outer member 110 and is mountedon the axle of the front wheel 2. The body side unit 200 includes theinner tube 210 and is mounted on the body 10. The front fork 21 alsoincludes a front-wheel spring 500. The front-wheel spring 500 isdisposed between the axle side unit 100 and the body side unit 200 toabsorb vibrations transmitted to the front wheel 2 caused by theroughness of a ground surface.

The outer member 110 and the inner tube 210 are coaxial, hollowcylindrical members. A direction of the center line (that is, an axialdirection) of each cylinder will be hereinafter occasionally referred toas “vertical direction”. In this case, the body 10 side willoccasionally be referred to the upper side, and the front wheel 2 sidewill occasionally be referred to as the lower side. By moving the axleside unit 100 and the body side unit 200 relative to each other in thevertical direction (axial direction), the front fork 21 absorbsvibrations caused by the roughness of the ground surface whilesupporting the front wheel 2.

Configuration of Axle Side Unit 100

The axle side unit 100 includes the outer member 110, an attenuationforce generation unit 130, a rod 150, and a rod holding member 160. Theouter member 110 is mounted on the axle of the front wheel 2. Theattenuation force generation unit 130 generates attenuation forceutilizing viscous resistance of oil. The rod 150 holds the attenuationforce generation unit 130. The rod holding member 160 holds thelower-side end of the rod 150.

Configuration of Attenuation Force Generation Unit 130

The attenuation force generation unit 130 includes a piston 131, anupper-end side valve 136, and a lower-end side valve 137. The piston 131defines an operating oil chamber 50, which is formed in the space insidea cylinder 230, described later. The upper-end side valve 136 isdisposed at the upper-side end of the piston 131. The lower-end sidevalve 137 is disposed at the lower-side end of the piston 131. Theattenuation force generation unit 130 also includes a piston bolt 140and a nut 145. The piston bolt 140 supports the piston 131, theupper-end side valve 136, the lower-end side valve 137, and othermembers. The nut 145 is screwed on the piston bolt 140 to determine thepositions of the piston 131, the upper-end side valve 136, the lower-endside valve 137, and other members.

The piston 131 is a hollow cylindrical member and has on its outersurface a hermetic member sealing the gap between the cylinder 230 andthe piston 131. The piston 131 also has a first through hole 132 and asecond through hole 133, which are through holes open in the axialdirection. The piston 131 includes first radial conduits 134 and secondradial conduits 135. The first radial conduits 134 radially extend atthe upper-side end of the piston 131 and communicate with the firstthrough hole 132. The second radial conduits 135 radially extend at thelower-side end of the piston 131 and communicate with the second throughhole 133. A non-limiting example of the number of each of the firstthrough holes 132 and the second through holes 133 is three. The threefirst through holes 132 and the three second through holes 133 are eachdisposed at equal intervals in a circumferential direction and atpositions respectively corresponding to the first through hole 132 andthe second through hole 133.

The piston bolt 140 includes the shaft 141 and a base 142. The shaft 141is disposed on an upper end side of the piston bolt 140 and has a solidcylindrical shape. The base 142 is disposed on a lower end side of thepiston bolt 140 and has a solid cylindrical shape of larger radius thana radius of the shaft 141. In the piston bolt 140, a depression 143 isformed over a depth from the lower-side end surface of the base 142 tothe shaft 141. At the upper-side end of the depression 143, a radialthrough hole 144 is formed. The radial through hole 144 radiallypenetrates the depression 143 to allow the depression 143 to communicatewith an outside of the shaft 141.

On the upper-side end of the nut 145, a female thread 146 is formed. Thefemale thread 146 receives a male thread of the piston bolt 140. Underthe female thread 146, a depression 147 is formed. The depression 147 isdepressed over a depth from the lower-side end surface of the nut 145,and has a solid cylindrical shape of larger radius than the radius ofthe root of the female thread 146. In the nut 145, a radial through hole148 is formed. The radial through hole 148 radially penetrates the nut145 to allow the outside of the nut 145 to communicate with thedepression 147.

With the configuration described hereinbefore, the attenuation forcegeneration unit 130 is held on the rod 150 with the male thread on theupper-side end of the rod 150 screwed on the female thread on thedepression 143 of the piston bolt 140. The piston 131 is in contact withthe inner surface of the cylinder 230 through the hermetic member on theouter surface of the piston 131. Thus, the piston 131 defines a firstoil chamber 51 and a second oil chamber 52 in the space inside thecylinder 230. The first oil chamber 51 is upper than the piston 131, andthe second oil chamber 52 is lower than the piston 131.0020, 0021

Configuration of Rod Holding Member 160

The rod holding member 160 has a plurality of solid cylindrical portionsof different diameters. Namely, the rod holding member 160 includes theupper-end-side solid cylindrical portion 161, a lower-end-side solidcylindrical portion 162, and an intermediate solid cylindrical portion163. The upper-end-side solid cylindrical portion 161 is disposed at theupper-side end of the rod holding member 160. The lower-end-side solidcylindrical portion 162 is disposed at the lower-side end of the rodholding member 160. The intermediate solid cylindrical portion 163 isdisposed between the upper-end-side solid cylindrical portion 161 andthe lower-end-side solid cylindrical portion 162.

The upper-end-side solid cylindrical portion 161 has the axialdepression 161 a, a radial depression 161 b, and a radial through hole161 c. The axial depression 161 a is depressed over a depth in the axialdirection from an upper-side end surface of the upper-end-side solidcylindrical portion 161. The radial depression 161 b is depressedradially throughout a circumference of the upper-end-side solidcylindrical portion 161 over a depth from an outer surface of theupper-end-side solid cylindrical portion 161. The radial through hole161 c penetrates the axial depression 161 a and the radial depression161 b in a radial direction.

The axial depression 161 a also has an inclined surface 161 e. Theinclined surface 161 e is inclined relative to the axial direction, thatis, an inner diameter of the inclined surface 161 e gradually decreasesin a lower side direction.

Configuration of Support-Member Holding Member 180

The support-member holding member 180 is a hollow cylindrical member.The support-member holding member 180 has a communication hole 182. Thecommunication hole 182 is formed at a position axially corresponding tothe radial depression 161 b of the rod holding member 160, and thusallows an inside of the support-member holding member 180 to communicatewith an outside of the support-member holding member 180.

In the axle side unit 100 with the configuration described hereinbefore,a reservoir chamber 40 (storage chamber) is defined between the innersurface of the outer member 110 and the outer surfaces of the rod 150and the support-member holding member 180. The reservoir chamber 40stores oil kept hermetic in the front fork 21. Configuration of BodySide Unit 200

The body side unit 200 includes the inner tube 210 and a cap 220. Theinner tube 210 has a hollow cylindrical shape with open ends. The cap220 is mounted on an upper-side end of the inner tube 210.

The body side unit 200 also includes the cylinder 230 and a hermeticmember 240. The cylinder 230 has a hollow cylindrical shape. Thehermetic member 240 is mounted on a lower-side end of the cylinder 230,and keeps space inside the cylinder 230 hermetic.

The body side unit 200 also includes a front-wheel spring lengthadjustment unit 250 and the front-wheel passage switch unit 300. Thefront-wheel spring length adjustment unit 250 supports the front-wheelspring 500 at its upper-side end and adjusts (changes) a length of thefront-wheel spring 500. The front-wheel passage switch unit 300 ismounted on an upper-side end of the cylinder 230 and selects a passagefor the oil.

The body side unit 200 also includes a front-wheel relative positiondetector 281 (see FIG. 11). The front-wheel relative position detector281 detects a relative position of an upper-side end support member 270relative to a base member 260, described later, of the front-wheelspring length adjustment unit 250.

Configuration of Cap 220

The cap 220 is an approximately hollow cylindrical member. On the outersurface of the cap 220, a male thread 221 is formed. The male thread 221is screwed on the female thread 213, which is formed on the inner tube210. On the inner surface of the cap 220, a female thread is formed thatreceives male threads on the front-wheel spring length adjustment unit250 and the front-wheel passage switch unit 300. The cap 220 is mountedon the inner tube 210 and holds the front-wheel spring length adjustmentunit 250 and the front-wheel passage switch unit 300.

The cap 220 includes an O ring 222. The O ring 222 keeps the spaceinside the inner tube 210 liquid tight.

Configuration of Front-Wheel Spring Length Adjustment Unit 250

The front-wheel spring length adjustment unit 250 includes the basemember 260 and the upper-side end support member 270. The base member260 is secured on the cap 220. The upper-side end support member 270supports the front-wheel spring 500 at its upper-side end, and ismovable in the axial direction relative to the base member 260. Thus,the upper-side end support member 270 adjusts the length of thefront-wheel spring 500.

The base member 260 is an approximately hollow cylindrical member. Thebase member 260 has a protrusion 260 b at an upper-side end of the basemember 260. The protrusion 260 b is a radially protruding part of acircumference of the base member 260. A discharge passage 41 is disposedbetween the protrusion 260 b and a lower-side end on an outer surface ofa support member 400, described later. The discharge passage 41 is forthe oil in the cylinder 230 to be discharged into the reservoir chamber40. A ring-shaped passage 61 is defined between an inner surface of thebase member 260 and an outer surface of the cylinder 230. Thering-shaped passage 61 has a ring shape.

The upper-side end support member 270 includes a hollow cylindricalportion 271 and an internally facing portion 272. The hollow cylindricalportion 271 has a hollow cylindrical shape. The internally facingportion 272 radially internally extends from the lower-side end of thehollow cylindrical portion 271. The upper-side end support member 270defines a jack chamber 60 in the space defined between the outer surfaceof the cylinder 230 and the lower-side end of the base member 260. Thejack chamber 60 stores oil for use in adjusting the relative position ofthe upper-side end support member 270 relative to the base member 260.

The hollow cylindrical portion 271 has a radial through hole 273. Theradial through hole 273 radially penetrates the hollow cylindricalportion 271 and thus allows an inside of the hollow cylindrical portion271 to communicate with an outside of the hollow cylindrical portion271. Through the radial through hole 273, the oil in the jack chamber 60is discharged into the reservoir chamber 40. In this manner, thedisplacement of the upper-side end support member 270 relative to thebase member 260 is limited.

The jack chamber 60 is supplied the oil in the cylinder 230 through thering-shaped passage 61, which is defined between the inner surface ofthe base member 260 and the outer surface of the cylinder 230. Thisconfiguration will be detailed later.

Configuration of Front-Wheel Relative Position Detector 281

The front-wheel relative position detector 281 (see FIG. 11) detects,for example, an amount of displacement of the upper-side end supportmember 270 in the vertical direction relative to the base member 260,that is, an amount of displacement of the upper-side end support member270 in the vertical direction relative to the body frame 11. In anon-limiting embodiment, a coil is wound around the outer surface of thebase member 260, and the upper-side end support member 270 is made ofmagnetic material. Based on an impedance of the coil, which changes inaccordance with the displacement of the upper-side end support member270 in the vertical direction relative to the base member 260, thefront-wheel relative position detector 281 detects the amount ofdisplacement of the upper-side end support member 270.

Configuration of Front-Wheel Passage Switch Unit 300

FIG. 3 is an enlarged view of part III illustrated in FIG. 2.

FIG. 4 is an enlarged view of part IV illustrated in FIG. 3.

The front-wheel passage switch unit 300 is a device that switches amonga first option, a second option, and a third option. In the firstoption, the front-wheel passage switch unit 300 supplies oil dischargedfrom a pump 600, described later, to the reservoir chamber 40. In thesecond option, the front-wheel passage switch unit 300 supplies the oildischarged from the pump 600 to the jack chamber 60. In the thirdoption, the front wheel passage switch unit 300 supplies the oilaccommodated in the jack chamber 60 to the reservoir chamber 40.

The front-wheel passage switch unit 300 includes a front-wheel solenoid310, a spherical valve body 321, a push rod 322, a valve-body seatmember 330, a coil spring 340, and a press member 350. The push rod 322presses the valve body 321. The valve-body seat member 330 has a restingsurface for the valve body 321. The press member 350 receives the springforce of the coil spring 340 to press the valve body 321 against theresting surface.

The front-wheel passage switch unit 300 also includes a ball 360, a coilspring 361, and a disc 362. The coil spring 361 applies axial urgingforce to the ball 360. The disc 362 is disposed between the ball 360 andthe coil spring 361. The front-wheel passage switch unit 300 alsoincludes a ball seat member 365 and an accommodation member 370. Theball seat member 365 has a resting surface for the ball 360. Theaccommodation member 370 accommodates the coil spring 361 and the disc362.

The front-wheel passage switch unit 300 also includes a valveaccommodation inner member 380, a valve accommodation outer member 390,and the support member 400. The valve accommodation inner member 380accommodates the valve body 321, the valve-body seat member 330, andother members. The valve accommodation outer member 390 is disposedoutside the valve accommodation inner member 380, and accommodates theball 360, the ball seat member 365, and other members. The supportmember 400 supports the valve accommodation inner member 380 and thevalve accommodation outer member 390.

The front-wheel passage switch unit 300 also includes a transmissionmember 410 and a coil spring 415. The transmission member 410 is mountedon the lower end of an operation rod 314, described later, of thefront-wheel solenoid 310, and transmits thrust of the front-wheelsolenoid 310 to the push rod 322. The coil spring 415 applies axialurging force to the transmission member 410.

Configuration of Front-Wheel Solenoid 310

The front-wheel solenoid 310 is a proportional solenoid that includes acoil 311, a core 312, a plunger 313, and an operation rod 314. The core312 is disposed inside the coil 311. The plunger 313 is guided by thecore 312. The operation rod 314 is coupled to the plunger 313.

The front-wheel solenoid 310 also includes a case 315 and a cover 316.The case 315 accommodates the coil 311, the core 312, the plunger 313,and other members. The cover 316 covers an opening of the case 315.

The case 315 includes a hollow cylindrical portion 315 a and aninternally facing portion 315 b. The hollow cylindrical portion 315 ahas a hollow cylindrical shape. The internally facing portion 315 bradially internally extends from the lower-side end of the hollowcylindrical portion 315 a. The internally facing portion 315 b has athrough hole through which the operation rod 314 is inserted. A guidebush 315 c is fitted with the internally facing portion 315 b to guidethe movement of the operation rod 314.

The operation rod 314 has a hollow cylindrical shape. At the upper-sideend, the operation rod 314 is accommodated in the case 315. At thelower-side end, the operation rod 314 protrudes from the case 315. Theportion of the operation rod 314 protruding from the case 315 isattached with a disc-shaped valve 317. The disc-shaped valve 317 opensand closes a passage, described later, formed in the valve accommodationinner member 380. A coil spring 318 surrounds the portion of theoperation rod 314 between the valve 317 and the case 315. The coilspring 318 applies an axial urging force to the valve 317.

With the configuration of the front-wheel solenoid 310 describedhereinbefore, the coil 311 is supplied a current through a connector anda lead that are mounted on the cap 220. The current causes the plunger313 to generate an axial thrust that accords with the amount of thecurrent. The thrust of the plunger 313 causes the operation rod 314,which is coupled to the plunger 313, to make an axial movement. In thefront-wheel solenoid 310 according to this embodiment, the plunger 313generates an amount of axial thrust that causes the operation rod 314 toprotrude from the case 315 by an amount that increases as the currentsupplied to the coil 31 increases.

The amount of the current supplied to the coil 311 is controlled by thecontroller 70.

Configuration of Valve-body Seat Member 330

The valve-body seat member 330 includes a conical portion 332 and asolid cylindrical portion 333. The conical portion 332 has an inclinedsurface 331. The inclined surface 331 is inclined relative to the axialdirection, that is, the outer diameter of the valve-body seat member 330gradually increases in the lower side direction. The solid cylindricalportion 333 has a solid cylindrical shape.

The conical portion 332 has an upper-end depression 334. The upper-enddepression 334 is depressed over a depth in the axial direction from anupper-side end surface of the conical portion 332. The solid cylindricalportion 333 has a lower-end depression 335 and a communication hole 336.The lower-end depression 335 is depressed over a depth in the axialdirection from a lower-side end surface of the solid cylindrical portion333. The communication hole 336 allows the lower-end depression 335 tocommunicate with the upper-end depression 334.

The lower-end depression 335 includes a conical depression 335 b and acylindrical depression 335 c. The conical depression 335 b, which has aconical shape, has an inclined surface 335 a. The inclined surface 335 ais inclined relative to the axial direction, that is, a radius of theconical depression 335 b gradually increases in the lower sidedirection. The cylindrical depression 335 c has a cylindrical shape.

The conical portion 332 has a groove 332 a on an outer surface of theconical portion 332. The groove 332 a is depressed radially throughout acircumference of the conical portion 332. An O ring 337 is fitted in thegroove 332 a to seal a gap between the conical portion 332 and the valveaccommodation inner member 380.

Configuration of Valve Accommodation Inner Member 380

The valve accommodation inner member 380 is an approximately solidcylindrical member with a flange formed at the upper-side end of thevalve accommodation inner member 380. The valve accommodation innermember 380 has an upper-end depression 381, a lower-end depression 382,and a communication hole 383. The upper-end depression 381 is depressedover a depth in the axial direction from the upper-side end surface ofthe valve accommodation inner member 380. The lower-end depression 382is depressed over a depth in the axial direction from the lower-side endsurface of the valve accommodation inner member 380. Through thecommunication hole 383, the upper-end depression 381 and the lower-enddepression 382 communicate with each other.

On the outer surface of the valve accommodation inner member 380, afirst radial depression 384 and a second radial depression 385 areformed. The first radial depression 384 and the second radial depression385 are depressed radially throughout the circumference of the valveaccommodation inner member 380.

The upper-end depression 381 has a solid cylindrical shape thataccommodates the transmission member 410 and the coil spring 415.

The lower-end depression 382 includes a first cylindrical depression 382a, a second cylindrical depression 382 b, and a conical depression 382c. The first cylindrical depression 382 a and the second cylindricaldepression 382 b have cylindrical shapes of different diameters. Theconical depression 382 c is formed between the first cylindricaldepression 382 a and the second cylindrical depression 382 b, and has aninclined surface inclined relative to the axial direction, that is, theradius of the conical depression 382 c gradually increases in the lowerside direction.

The valve accommodation inner member 380 has a plurality of first radialcommunication holes 387, which are formed at equal intervals in thecircumferential direction. Each first radial communication hole 387 is aradial through hole through which the first cylindrical depression 382 aof the lower-end depression 382 and the first radial depression 384communicate with each other.

The valve accommodation inner member 380 has a plurality of secondradial communication holes 388, which are formed at equal intervals inthe circumferential direction. Each second radial communication hole 388is a radial through hole through which the second cylindrical depression382 b and the outside of the valve accommodation inner member 380communicate with each other.

The valve accommodation inner member 380 has a plurality of inner axialcommunication holes 389 a formed at equal intervals in thecircumferential direction. Each inner axial communication hole 389 a isan axial through hole through which the upper-side end of the valveaccommodation inner member 380 and the first radial depression 384communicate with each other.

The valve accommodation inner member 380 has a plurality of outer axialcommunication holes 389 b formed at equal intervals in thecircumferential direction. The outer axial communication holes 389 baxially penetrate the flange.

Configuration of Valve Accommodation Outer Member 390

The valve accommodation outer member 390 includes a first hollowcylindrical portion 391, a second hollow cylindrical portion 392, and aflange. The first hollow cylindrical portion 391 and the second hollowcylindrical portion 392 have cylindrical shapes of different diameters.The flange extends radially outwardly from the upper-side end of thefirst hollow cylindrical portion 391. The first hollow cylindricalportion 391 has an outer diameter larger than the outer diameter of thesecond hollow cylindrical portion 392.

The valve accommodation outer member 390 has an upper-end depression393. The upper-end depression 393 is depressed over a depth in the axialdirection from the upper-side end surface of the valve accommodationouter member 390.

The first hollow cylindrical portion 391 has a plurality of axialcommunication holes 394, which are formed at equal intervals in thecircumferential direction. Each axial communication hole 394 allows theupper-end depression 393 to communicate with the space that is below thefirst hollow cylindrical portion 391 and defined between the outersurface of the second hollow cylindrical portion 392 and the innersurface of the cylinder 230.

The first hollow cylindrical portion 391 has a plurality of first radialcommunication holes 397 and a plurality of second radial communicationholes 398. The first radial communication holes 397 and the secondradial communication holes 398 are radial through holes that allow aninside of the first hollow cylindrical portion 391 to communicate withan outside of the first hollow cylindrical portion 391. The first radialcommunication holes 397 and the second radial communication holes 398are formed at equal intervals in the circumferential direction and atpositions on the first hollow cylindrical portion 391 where no axialcommunication holes 394 are formed.

With the configuration of the front-wheel passage switch unit 300described hereinbefore, when supply of current to the coil 311 of thefront-wheel solenoid 310 is stopped or when the current supplied to thecoil 311 is less than a predetermined first reference current, the valve317, which is mounted on the operation rod 314, does not rest on theupper-side end surface of the valve accommodation inner member 380. Thisreleases open the opening on the upper end side of the inner axialcommunication hole 389 a, which is formed in the valve accommodationinner member 380.

When the current supplied to the coil 311 of the front-wheel solenoid310 is equal to or higher than the first reference current, theoperation rod 314 moves in the lower side direction to make the valve317, which is mounted on the operation rod 314, rest on the upper-sideend surface of the valve accommodation inner member 380 to close theopening on the upper end side of the inner axial communication hole 389a.

When the current supplied to the coil 311 of the front-wheel solenoid310 is equal to or higher than a predetermined second reference current,which is higher than the first reference current, the operation rod 314moves further in the lower side direction. Then, the operation rod 314pushes the push rod 322 in the lower side direction through thetransmission member 410. When the push rod 322 is pushed in the lowerside direction, the valve body 321 is pushed by the push rod 322 awayfrom the inclined surface 335 a of the lower-end depression 335 of thevalve-body seat member 330.

When the supply of current to the coil 311 is stopped or when thecurrent supplied to the coil 311 is less than the first referencecurrent, the valve 317, which is mounted on the operation rod 314,releases the inner axial communication hole 389 a, which is formed inthe valve accommodation inner member 380, and the valve body 321 restson the inclined surface 335 a of the lower-end depression 335 of thevalve-body seat member 330. This state will be hereinafter referred toas first switch state.

When the current supplied to the coil 311 is equal to or higher than thefirst reference current and less than the second reference current, thevalve 317, which is mounted on the operation rod 314, closes the inneraxial communication hole 389 a, which is formed in the valveaccommodation inner member 380, and the valve body 321 rests on theinclined surface 335 a of the lower-end depression 335 of the valve-bodyseat member 330. This state will be hereinafter referred to as secondswitch state.

When the current supplied to the coil 311 is equal to or higher than thesecond reference current and less than a third reference current, thevalve 317, which is mounted on the operation rod 314, closes the inneraxial communication hole 389 a, which is formed in the valveaccommodation inner member 380, and the valve body 321 is away from theinclined surface 335 a of the lower-end depression 335 of the valve-bodyseat member 330. This state will be hereinafter referred to as a thirdswitch state.

The first reference current and the second reference current arerespectively 0.1 A and 0.5 A, for example. The maximum current flowingto the coil 311 of the front-wheel solenoid 310 is 3.2 A, for example.

When the current supplied to the coil 311 is equal to or higher than thethird reference current, the valve 317, which is mounted on theoperation rod 314, closes the inner axial communication hole 389 a,which is formed in the valve accommodation inner member 380, and theinclined surface 331 of the conical portion 332 of the valve-body seatmember 330 is away from the inclined surface on the conical depression382 c of the valve accommodation inner member 380. This state will behereinafter referred to as fourth switch state. In the fourth switchstate, the valve body 321 rests on the inclined surface 335 a of thelower-end depression 335 of the valve-body seat member 330.

Operation of Front Fork 21

With the configuration of the front fork 21 described hereinbefore, thefront-wheel spring 500 supports the weight of the motorcycle 1 and thusabsorbs impact. The attenuation force generation unit 130 attenuates thevibration in the front-wheel spring 500.

FIG. 5 illustrates how the front fork 21 operates at the time of acompression stroke.

In the compression stroke of the front fork 21, the piston 131 of theattenuation force generation unit 130 moves in the upper-side directionrelative to the cylinder 230 as indicated by the outlined arrow. Themovement of the piston 131 causes the oil in the first oil chamber 51 tobe pressurized. This causes the lower-end side valve 137 covering thefirst through hole 132 to open and the oil to flow into the second oilchamber 52 through the first through hole 132 (see arrow C1). The oilflow from the first oil chamber 51 to the second oil chamber 52 isnarrowed through the first through hole 132 and the lower-end side valve137. This causes attenuation force for the compression stroke to begenerated.

At the time of the compression stroke, the rod 150 enters the cylinder230. The entry causes an amount of oil corresponding to the volume ofthe rod 150 in the cylinder 230 to be supplied to the jack chamber 60 orthe reservoir chamber 40, which depends on the switch state selected bythe front-wheel passage switch unit 300 (see arrow C2). The switch stateselected by the front-wheel passage switch unit 300 as to which of thejack chamber 60 and the reservoir chamber 40 to supply the oil will bedescribed later. Here, the attenuation force generation unit 130, therod 150, the cylinder 230, and other elements function as a pump tosupply the oil in the cylinder 230 to the jack chamber 60 or thereservoir chamber 40. In the following description, this pump willoccasionally be referred to as “pump 600”.

FIG. 6 illustrates how the front fork 21 operates at the time of arebound stroke.

In the rebound stroke of the front fork 21, the piston 131 of theattenuation force generation unit 130 moves in the lower-side directionrelative to the cylinder 230 as indicated by the outlined arrow. Themovement of the piston 131 causes the oil in the second oil chamber 52to be pressurized. This causes the upper-end side valve 136 covering thesecond through hole 133 to open and the oil to flow into the first oilchamber 51 through the second through hole 133 (see arrow T1). The oilflow from the second oil chamber 52 to the first oil chamber 51 isnarrowed through the second through hole 133 and the upper-end sidevalve 136. This causes attenuation force for the rebound stroke to begenerated.

At the time of the rebound stroke, the rod 150 withdraws from thecylinder 230. The withdrawal causes an amount of oil corresponding tothe volume of the rod 150 that has been in the cylinder 230 to besupplied from the reservoir chamber 40 to the first oil chamber 51. Thatis, the movement of the piston 131 in the lower-side direction causesthe first oil chamber 51 to be depressurized and the oil in thereservoir chamber 40 to enter the first oil chamber 51. Specifically,the oil in the reservoir chamber 40 passes through the communicationhole 182 of the support-member holding member 180 and the radial throughhole 161 c of the rod holding member 160, and enters the axialdepression 161 a of the rod holding member 160. Then, the oil moves theball 166 in the upper-side direction and enters the rod 150 (see arrowT2). In the rod 150, the oil passes through the depression 143 of thepiston bolt 140, the radial through hole 144, and the radial throughhole 148 of the nut 145, and reaches the first oil chamber 51 (see arrowT3).

Thus, the communication hole 182 of the support-member holding member180, the radial through hole 161 c of the rod holding member 160, theaxial depression 161 a of the rod holding member 160, an inside of therod 150, the depression 143 of the piston bolt 140, the radial throughhole 144, and the radial through hole 148 of the nut 145 function asintake passages through which the oil is taken from the reservoirchamber 40 into the cylinder 230 (first oil chamber 51). The ball 166and the inclined surface 161 e, which is formed on the axial depression161 a of the rod holding member 160, function as a check valve thatallows the oil to flow from the reservoir chamber 40 into the inside ofthe rod 150 and that limits discharge of the oil from the inside of therod 150 to the reservoir chamber 40.

FIG. 7 illustrates a flow of oil in the front-wheel passage switch unit300 in the first switch state.

When the front-wheel passage switch unit 300 is in the first switchstate at the time of the compression stroke of the front fork 21, oildischarged from the pump 600, which is made up of members such as theattenuation force generation unit 130, the rod 150, and the cylinder230, flows in the upper side direction through the axial communicationholes 394, which are formed in the valve accommodation outer member 390as indicated by arrow P1 in FIG. 7. The oil that has flowed in the upperside direction through the axial communication holes 394, which areformed in the valve accommodation outer member 390, flows in the upperside direction through the outer axial communication hole 389 b of thevalve accommodation inner member 380, and then flows in the lower sidedirection through the inner axial communication hole 389 a, which isopen. Then, the oil flows to the reservoir chamber 40 through the firstradial communication holes 397, which are formed in the valveaccommodation outer member 390, and through the discharge passage 41,which is defined between the protrusion 260 b of the base member 260 andthe lower-side end of the support member 400.

Thus, the axial communication holes 394 of the valve accommodation outermember 390, the outer axial communication hole 389 b and the inner axialcommunication hole 389 a of the valve accommodation inner member 380,the first radial communication holes 397 of the valve accommodationouter member 390, and the discharge passage 41 function as a firstcommunication passage R1 (see FIG. 11). Through the first communicationpassage R1, the cylinder 230 and the reservoir chamber 40 communicatewith each other. The valve 317, which is mounted on the operation rod314, the coil spring 318, and the upper-side end of the valveaccommodation inner member 380 function as a first communication passageswitch valve V1 (see FIG. 11). The first communication passage switchvalve V1 opens and closes the first communication passage R1.

FIG. 8 illustrates a flow of oil in the front-wheel passage switch unit300 in the second switch state.

When the front-wheel passage switch unit 300 is in the second switchstate at the time of the compression stroke of the front fork 21, thevalve 317, which is mounted on the operation rod 314, closes the inneraxial communication hole 389 a, which is formed in the valveaccommodation inner member 380. This causes the oil discharged from thepump 600 to flow to the jack chamber 60 as indicated by arrow P2 in FIG.8. Specifically, the oil discharged from the pump 600 pushes up the ball360 against the urging force of the coil spring 361, and flows in theupper side direction through the gap between the outer surface of thevalve accommodation inner member 380 and the inner surface of the valveaccommodation outer member 390 and the gap between the outer surface ofthe accommodation member 370 and the inner surface of the valveaccommodation outer member 390. Then, the oil flows to the outside ofthe valve accommodation outer member 390 through the second radialcommunication holes 398 of the valve accommodation outer member 390. Theoil that has passed through the second radial communication holes 398flows to the jack chamber 60 through the ring-shaped passage 61, whichis defined between the outer surface of the cylinder 230 and the innersurface of the base member 260 of the front-wheel spring lengthadjustment unit 250.

Thus, the gap between the outer surface of the valve accommodation innermember 380 and the inner surface of the valve accommodation outer member390, the gap between the outer surface of the accommodation member 370and the inner surface of the valve accommodation outer member 390, thesecond radial communication holes 398 of the valve accommodation outermember 390, and the ring-shaped passage 61 function as a secondcommunication passage R2 (see FIG. 11). Through the second communicationpassage R2, the cylinder 230 and the jack chamber 60 communicate witheach other. The ball 360, the coil spring 361, the disc 362, and theball seat member 365 function as a second communication passage switchvalve V2 (see FIG. 11). The second communication passage switch valve V2opens and closes the second communication passage R2. The secondcommunication passage switch valve V2 also functions as a check valvethat allows oil to flow from the inside of the cylinder 230 into thejack chamber 60 and that inhibits the oil from flowing from the jackchamber 60 into the cylinder 230.

FIG. 9 illustrates a flow of oil in the front-wheel passage switch unit300 in the third switch state.

When the front-wheel passage switch unit 300 is in the third switchstate at the time of the compression stroke of the front fork 21, theoil in the jack chamber 60 flows to the reservoir chamber 40 asindicated by arrow P3 in FIG. 9. Specifically, the oil in the jackchamber 60 enters the lower-end depression 382 of the valveaccommodation inner member 380 through the ring-shaped passage 61, whichis defined between the outer surface of the cylinder 230 and the innersurface of the base member 260 of the front-wheel spring lengthadjustment unit 250, through the second radial communication holes 398of the valve accommodation outer member 390, and through the secondradial communication holes 388 of the valve accommodation inner member380. The oil that has entered the lower-end depression 382 of the valveaccommodation inner member 380 flows in the lower side direction throughthe gap between the valve accommodation inner member 380 and the outersurface of the solid cylindrical portion 333 of the valve-body seatmember 330, and enters the lower-end depression 335 of the valve-bodyseat member 330. The oil that has entered the lower-end depression 335of the valve-body seat member 330 flows in the upper side directionthrough the gap between the press member 350 and the valve body 321 andthe gap between the push rod 322 and the valve-body seat member 330, andpasses through the first radial communication holes 387 of the valveaccommodation inner member 380. The oil that has passed through thefirst radial communication holes 387 of the valve accommodation innermember 380 flows to the reservoir chamber 40 through the first radialcommunication holes 397, which are formed in the valve accommodationouter member 390, and through the discharge passage 41, which is definedbetween the protrusion 260 b of the base member 260 and the lower-sideend of the support member 400.

Thus, the ring-shaped passage 61, the second radial communication holes398 of the valve accommodation outer member 390, the second radialcommunication holes 388 of the valve accommodation inner member 380, thegap between the valve accommodation inner member 380 and the outersurface of the solid cylindrical portion 333 of the valve-body seatmember 330, the gap between the press member 350 and the valve body 321,the gap between the push rod 322 and the valve-body seat member 330, thefirst radial communication holes 387 of the valve accommodation innermember 380, the first radial communication holes 397 of the valveaccommodation outer member 390, and the discharge passage 41 function asa third communication passage R3 (see FIG. 11). Through the thirdcommunication passage R3, the jack chamber 60 and the reservoir chamber40 communicate with each other. The valve body 321 and the inclinedsurface 335 a of the lower-end depression 335 of the valve-body seatmember 330 function as a third communication passage switch valve V3(see FIG. 11). The third communication passage switch valve V3 opens andcloses the third communication passage R3.

FIG. 10 illustrates a flow of oil in the front-wheel passage switch unit300 in the fourth switch state.

When the front-wheel passage switch unit 300 is in the fourth switchstate at the time of the compression stroke of the front fork 21, theoil in the jack chamber 60 flows to the reservoir chamber 40 asindicated by arrow P4 in FIG. 10. Specifically, the oil in the jackchamber 60 enters the lower-end depression 382 of the valveaccommodation inner member 380 through the ring-shaped passage 61, thesecond radial communication holes 398 of the valve accommodation outermember 390, and the second radial communication holes 388 of the valveaccommodation inner member 380. The oil that has entered the lower-enddepression 382 of the valve accommodation inner member 380 flows in theupper side direction through the gap defined by the inclined surface 331of the conical portion 332 of the valve-body seat member 330, the O ring337, and the inclined surface on the conical depression 382 c of thevalve accommodation inner member 380, and passes through the firstradial communication holes 387 of the valve accommodation inner member380. The oil that has passed the first radial communication holes 387 ofthe valve accommodation inner member 380 flows to the reservoir chamber40 through the first radial communication holes 397, which are formed inthe valve accommodation outer member 390, and through the dischargepassage 41, which is defined between the protrusion 260 b of the basemember 260 and the lower-side end of the support member 400.

Thus, the ring-shaped passage 61, the second radial communication holes398 of the valve accommodation outer member 390, the second radialcommunication holes 388 of the valve accommodation inner member 380, thegap defined by the inclined surface 331 of the valve-body seat member330, the O ring 337, and the inclined surface on the conical depression382 c of the valve accommodation inner member 380, the first radialcommunication holes 387 of the valve accommodation inner member 380, thefirst radial communication holes 397 of the valve accommodation outermember 390, and the discharge passage 41 function as a fourthcommunication passage R4 (not illustrated). Through the fourthcommunication passage R4, the jack chamber 60 and the reservoir chamber40 communicate with each other. The inclined surface 331 of the conicalportion 332 of the valve-body seat member 330, the O ring 337, and theinclined surface on the conical depression 382 c of the valveaccommodation inner member 380 function as a fourth communicationpassage switch valve V4 (not illustrated). The fourth communicationpassage switch valve V4 opens and closes the fourth communicationpassage R4.

Change from Third Switch State to Fourth Switch State of Front-WheelPassage Switch Unit 300

When the front-wheel passage switch unit 300 is in the third switchstate, the oil in the jack chamber 60 flows to the reservoir chamber 40as indicated by arrow P3 illustrated in FIG. 9. This flow of the oilcauses the amount of the oil in the jack chamber 60 to decrease, causinga reduction in length of the front-wheel spring 500. The reduction inlength of the spring 500 causes the pressure in the jack chamber 60 todecrease. As a result, the pressure in a back pressure chamber definedbetween the valve-body seat member 330 and the accommodation member 370at the time when the front-wheel passage switch unit 300 is in the thirdswitch state is lower than the pressure in the back pressure chamber atthe time when the front-wheel passage switch unit 300 is in the secondswitch state. This causes the valve-body seat member 330 to start tomove in the lower side direction.

When the coil 311 of the front-wheel solenoid 310 is supplied a currentthat is equal to or higher than the third reference current, the pushrod 322 moves the valve body 321 further in the lower side directionthan when the passage switch unit 300 is in the third switch state. Thisenlarges the gap between the valve body 321 and the inclined surface 335a of the lower-end depression 335 of the valve-body seat member 330. Asa result, the pressure in the jack chamber 60 further decreases, causinga further decrease in the pressure in the back pressure chamber. Thefurther decrease in the pressure in the back pressure chamber causes thevalve-body seat member 330 to move in the lower side direction. Thiscauses the inclined surface 331 of the conical portion 332 of thevalve-body seat member 330 to move away from the inclined surface on theconical depression 382 c of the valve accommodation inner member 380.Thus, the third switch state changes to the fourth switch state.

Communication Passages Open or Closed in Accordance with Switch StateSelected by Front-Wheel Passage Switch Unit 300

FIG. 11A illustrates whether the first communication passage R1, thesecond communication passage R2, and the third communication passage R3are open or closed when the front-wheel passage switch unit 300 is inthe first switch state. FIG. 11B illustrates whether the firstcommunication passage R1, the second communication passage R2, and thethird communication passage R3 are open or closed when the front-wheelpassage switch unit 300 is in the second switch state. FIG. 11Cillustrates whether the first communication passage R1, the secondcommunication passage R2, and the third communication passage R3 areopen or closed when the front-wheel passage switch unit 300 is in thethird switch state.

As illustrated in FIG. 11A, when the current supplied to the coil 311 ofthe front-wheel solenoid 310 is less than the first reference current,the front-wheel passage switch unit 300 is in the first switch state.That is, the first communication passage switch valve V1 is open and thethird communication passage switch valve V3 is closed. This causes theoil discharged from the pump 600 to reach the reservoir chamber 40through the first communication passage R1. In this case, the oildischarged from the pump 600 does not have such a high pressure as toopen the second communication passage switch valve V2. Hence, the oildoes not flow through the second communication passage R2. In otherwords, since the first communication passage switch valve V1 is open,the second communication passage switch valve V2 is closed. In the firstswitch state, the oil in the jack chamber 60 does not increase ordecrease.

As illustrated in FIG. 11B, when the current supplied to the coil 311 ofthe front-wheel solenoid 310 is equal to or higher than the firstreference current and less than the second reference current, thefront-wheel passage switch unit 300 is in the second switch state. Thatis, the first communication passage switch valve V1 and the thirdcommunication passage switch valve V3 are closed. Thus, the oildischarged from the pump 600 opens the second communication passageswitch valve V2 to reach the jack chamber 60 through the secondcommunication passage R2. In the second switch state, the amount of theoil in the jack chamber 60 increases.

As illustrated in FIG. 11C, when the current supplied to the coil 311 ofthe front-wheel solenoid 310 is equal to or higher than the secondreference current and less than the third reference current, thefront-wheel passage switch unit 300 is in the third switch state. Thatis, the first communication passage switch valve V1 is closed and thethird communication passage switch valve V3 is open. This causes the oilin the jack chamber 60 to reach the reservoir chamber 40 through thethird communication passage R3. In the third switch state, the amount ofthe oil in the jack chamber 60 decreases.

When the current supplied to the coil 311 of the front-wheel solenoid310 is equal to or higher than the third reference current, thefront-wheel passage switch unit 300 is in the fourth switch state. Thatis, the first communication passage switch valve V1 is closed and thefourth communication passage switch valve V4 is open. This causes theoil in the jack chamber 60 to reach the reservoir chamber 40 through thefourth communication passage R4.

The passage defined in the fourth switch state by the gap defined by theinclined surface 331 of the conical portion 332 of the valve-body seatmember 330, the O ring 337, and the inclined surface on the valveaccommodation inner member 380 is wider than the passage defined in thethird switch state by the gap between the valve accommodation innermember 380 and the outer surface of the solid cylindrical portion 333 ofthe valve-body seat member 330.

The passage defined in the third switch state by the gap between thevalve body 321 and the inclined surface 335 a on the valve-body seatmember 330 is narrower than the passage defined in the third switchstate by the gap between the valve accommodation inner member 380 andthe outer surface of the solid cylindrical portion 333 of the valve-bodyseat member 330. Therefore, when the passage switch unit 300 is in thefourth switch state, the amount of the oil in the jack chamber 60decreases more quickly than when the passage switch unit 300 is in thethird switch state.

Up-and-Down of Vehicle Height

In the front fork 21 operating in the above-described manner, when thefront-wheel passage switch unit 300 is in the second switch state, theoil discharged from the pump 600 at the time of the compression strokeflows into the jack chamber 60, increasing the amount of oil in the jackchamber 60. The increase in the amount of oil in the jack chamber 60causes the upper-side end support member 270 to move in the lower-sidedirection relative to the base member 260 of the front-wheel springlength adjustment unit 250. The movement of the upper-side end supportmember 270 in the lower-side direction relative to the base member 260causes the spring length of the front-wheel spring 500 to shorten. Theshortened spring length of the front-wheel spring 500 causes the springforce of the front-wheel spring 500 in pressing the upper-side endsupport member 270 to increase as compared with the spring force beforethe movement of the upper-side end support member 270 relative to thebase member 260. This causes an increase in preset load (pre-load),which is an amount of load that keeps the position of the body frame 11unchanged relative to the position of the front wheel 2 even when forceacts from the body frame 11 toward the front wheel 2 side. In this case,the amount of depression of the front fork 21 is smaller when the sameamount of force acts in the axial direction from the body frame 11 (seat19) side. Thus, when the spring length of the front-wheel spring 500 isshortened due to the movement of the upper-side end support member 270relative to the base member 260, the height of the seat 19 increases ascompared with the height of the seat 19 before the movement of theupper-side end support member 270 relative to the base member 260 (thatis, the vehicle height increases).

When the front-wheel passage switch unit 300 is in the third switchstate or the fourth switch state, the amount of oil in the jack chamber60 decreases. The decrease in the amount of oil causes the upper-sideend support member 270 to move in the upper-side direction relative tothe base member 260 of the front-wheel spring length adjustment unit250. The movement of the upper-side end support member 270 in theupper-side direction relative to the base member 260 causes the springlength of the front-wheel spring 500 to increase. The increased springlength of the front-wheel spring 500 causes the spring force of thefront-wheel spring 500 in pressing the upper-side end support member 270to reduce as compared with the spring force before the movement of theupper-side end support member 270 relative to the base member 260. Thiscauses the preset load (pre-load) to decrease, and the amount ofdepression of the front fork 21 is larger when the same amount of forceacts in the axial direction from the body frame 11 (seat 19) side. Thus,when the spring length of the front-wheel spring 500 is increased due tothe movement of the upper-side end support member 270 in the upper-sidedirection relative to the base member 260, the height of the seat 19decreases as compared with the height of the seat 19 before the movementof the upper-side end support member 270 relative to the base member 260(that is, the vehicle height decreases). When the front-wheel passageswitch unit 300 is in the fourth switch state, the amount of the oil inthe jack chamber 60 decreases more quickly than when the front-wheelpassage switch unit 300 is in the third switch state, as describedabove. Hence, when the front-wheel passage switch unit 300 is in thefourth switch state, the vehicle height decreases more quickly than whenthe front-wheel passage switch unit 300 is in the third switch state.

When the front-wheel passage switch unit 300 is in the first switchstate, the oil discharged from the pump 600 at the time of thecompression stroke flows into the reservoir chamber 40, and thus theamount of oil in the jack chamber 60 does not increase or decrease.Thus, the height of the seat 19 is maintained (that is, the vehicleheight is maintained).

Configuration of Rear Suspension 22

The rear suspension 22 is disposed between the body 10 and the rearwheel 3 of the motorcycle 1, and supports the rear wheel 3. The rearsuspension 22 includes an axle side unit, a body side unit, and arear-wheel spring 502 (see FIG. 1). The axle side unit is mounted on theaxle of the rear wheel 3. The body side unit is mounted on the body 10.The rear-wheel spring 502 is disposed between the axle side unit and thebody side unit, and absorbs vibrations transmitted to the rear wheel 3caused by the roughness of the ground surface. The rear-wheel spring 502has an upper-side end supported on the body side unit and has alower-side end supported on the axle side unit.

The axle side unit includes an attenuation force generation unit, a rod152 (see FIG. 1), and a spring lower-side end support member 153 (seeFIG. 1). The attenuation force generation unit generates attenuationforce utilizing viscous resistance of oil. The rod 152 holds theattenuation force generation unit. The spring lower-side end supportmember 153 supports the lower-side end of the rear-wheel spring 502.

The body side unit includes a cylinder 232 (see FIG. 1), a rear-wheelspring length adjustment unit 252 (see FIG. 1), and a rear-wheel passageswitch unit 302 (see FIG. 1). The attenuation force generation unit isinserted in the cylinder 232. The rear-wheel spring length adjustmentunit 252 supports an upper-side end of the rear-wheel spring 502 toadjust (change) a length of the rear-wheel spring 502. The rear-wheelpassage switch unit 302 is mounted outside of the cylinder 232 to switchamong the passages of the oil.

The rear suspension 22 also includes a reservoir chamber (which is thestorage chamber) and a pump. The reservoir chamber stores the oil. Thepump includes the cylinder 232. When a relative distance between thebody 10 and the rear wheel 3 increases, the pump takes into the cylinder232 the oil stored in the reservoir chamber. When the relative distancebetween the body 10 and the rear wheel 3 decreases, the pump dischargesthe oil out of the cylinder 232.

Similarly to the front-wheel spring length adjustment unit 250 of thefront fork 21, the rear-wheel spring length adjustment unit 252 includesa base member 253 (see FIG. 1) and an upper-side end support member 254(see FIG. 1). The base member 253 is secured to a side of the body frame11. The upper-side end support member 254 supports an upper-side end ofthe rear-wheel spring 502 and moves in the axial direction relative tothe base member 253 so as to change the length of the rear-wheel spring502. The rear-wheel spring length adjustment unit 252 includes a jackchamber (which is the accommodation chamber) that accommodates the oil.The upper-side end support member 254 supports the upper-side end of therear-wheel spring 502. The rear-wheel spring length adjustment unit 252adjusts the length of the rear-wheel spring 502 in accordance with anamount of the oil in the jack chamber.

The rear suspension 22 also includes a rear-wheel relative positiondetector 282 (see FIG. 12) to detect a relative position, relative tothe body frame 11, of the member that supports the upper-side end of therear-wheel spring 502. In a non-limiting embodiment, the rear-wheelrelative position detector 282 detects an amount of displacement of theupper-side end support member 254 in the axial direction relative to thebase member 253, that is, an amount of displacement of the upper-sideend support member 254 in the axial direction relative to the body frame11. In a non-limiting embodiment, a coil is wound around an outersurface of the base member 253, and the upper-side end support member254 is made of magnetic material. Based on an impedance of the coil,which changes in accordance with displacement of the upper-side endsupport member 254 in the vertical direction relative to the base member253, the rear-wheel relative position detector 282 detects an amount ofdisplacement of the upper-side end support member 254.

Communication Passages Open or Closed in Accordance with Switch StateSelected by Rear-Wheel Passage Switch Unit 302

The rear-wheel passage switch unit 302 has a configuration and functionssimilar to the configuration and functions of the front-wheel passageswitch unit 300 of the front fork 21. Specifically, the rear-wheelpassage switch unit 302 includes a first communication passage R1, asecond communication passage R2, and a third communication passage R3.The first communication passage R1 allows the inside of the cylinder 232and the reservoir chamber to communicate with each other. The secondcommunication passage R2 allows the inside of the cylinder 232 and thejack chamber to communicate with each other. The third communicationpassage R3 allows the jack chamber and the reservoir chamber tocommunicate with each other. The rear-wheel passage switch unit 302 alsoincludes a first communication passage switch valve V1, a secondcommunication passage switch valve V2, and a third communication passageswitch valve V3. The first communication passage switch valve V1 opensand closes the first communication passage R1. The second communicationpassage switch valve V2 opens and closes the second communicationpassage R2. The third communication passage switch valve V3 opens andcloses the third communication passage R3.

When the current supplied to the rear-wheel passage switch unit 302 isless than a predetermined first reference current, the rear-wheelpassage switch unit 302 opens the first communication passage R1 andcloses the third communication passage R3. When the current supplied tothe rear-wheel passage switch unit 302 is equal to or higher than thefirst reference current and less than a second reference current, therear-wheel passage switch unit 302 closes the first communicationpassage R1 and the third communication passage R3. When the currentsupplied to the rear-wheel passage switch unit 302 is equal to or higherthan the second reference current, the rear-wheel passage switch unit302 opens the third communication passage R3 and closes the firstcommunication passage R1.

Specifically, when the current supplied to the rear-wheel passage switchunit 302 is less than the predetermined first reference current, therear-wheel passage switch unit 302 allows the inside of the cylinder 232and the reservoir chamber to communicate with each other to guide theoil discharged from the pump into the reservoir chamber. When thecurrent supplied to the rear-wheel passage switch unit 302 is equal toor higher than the first reference current and less than the secondreference current, the rear-wheel passage switch unit 302 allows theinside of the cylinder 232 and the jack chamber to communicate with eachother to guide the oil discharged from the pump into the jack chamber.When the current supplied to the rear-wheel passage switch unit 302 isequal to or higher than the second reference current, the rear-wheelpassage switch unit 302 allows the jack chamber and the reservoirchamber to communicate with each other to guide the oil accommodated inthe jack chamber into the reservoir chamber.

More specifically, when the current supplied to a coil of a rear-wheelsolenoid of the rear-wheel passage switch unit 302 is less than thefirst reference current, the rear-wheel passage switch unit 302 is in afirst switch state, in which the first communication passage switchvalve V1 is open and the third communication passage switch valve V3 isclosed. This causes the oil discharged from the pump to reach thereservoir chamber through the first communication passage R1. In thiscase, since the oil discharged from the pump does not have such a highpressure as to open the second communication passage switch valve V2,the oil does not flow through the second communication passage R2. Inother words, since the first communication passage switch valve V1 isopen, the second communication passage switch valve V2 is closed. In thefirst switch state, the oil in the jack chamber does not increase nordecrease, and consequently, the vehicle height remains unchanged.

When the current supplied to the coil of the rear-wheel solenoid of therear-wheel passage switch unit 302 is equal to or higher than the firstreference current and less than the second reference current, therear-wheel passage switch unit 302 is in a second switch state, in whichthe first communication passage switch valve V1 and the thirdcommunication passage switch valve V3 are closed. This causes the oildischarged from the pump to open the second communication passage switchvalve V2 and reach the jack chamber. In the second switch state, theamount of oil in the jack chamber increases to increase the vehicleheight.

When the current supplied to the coil of the rear-wheel solenoid of therear-wheel passage switch unit 302 is equal to or higher than the secondreference current and less than the third reference current, therear-wheel passage switch unit 302 is in a third switch state, in whichthe first communication passage switch valve V1 is closed and the thirdcommunication passage switch valve V3 is open. This causes the oil inthe jack chamber to reach the reservoir chamber through the thirdcommunication passage R3. In the third switch state, the amount of oilin the jack chamber decreases to decrease the vehicle height.

When the current supplied to the coil of the rear-wheel solenoid of therear-wheel passage switch unit 302 is equal to or higher than the thirdreference current, the rear-wheel passage switch unit 302 is in a fourthswitch state, in which the first communication passage switch valve V1is closed and the fourth communication passage switch valve V4 is open.This causes the oil in the jack chamber to reach the reservoir chamberthrough the fourth communication passage R4. In the fourth switch state,the amount of oil in the jack chamber decreases more quickly to decreasethe vehicle height more quickly than in the third switch state.

Configuration of Controller 70

The controller 70 will be described below.

FIG. 12 is a block diagram of the controller 70.

The controller 70 includes a CPU, a ROM, and a RAM. The ROM storesprograms to be executed in the CPU and various kinds of data. The RAM isused as, for example, an operation memory for the CPU. The controller 70receives inputs such as signals output from the front-wheel rotationdetection sensor 31, the rear-wheel rotation detection sensor 32, thefront-wheel relative position detector 281, and the rear-wheel relativeposition detector 282.

The controller 70 includes a front-wheel rotation speed calculator 71and a rear-wheel rotation speed calculator 72. The front-wheel rotationspeed calculator 71 calculates the rotation speed of the front wheel 2based on an output signal from the front-wheel rotation detection sensor31. The rear-wheel rotation speed calculator 72 calculates the rotationspeed of the rear wheel 3 based on an output signal from the rear-wheelrotation detection sensor 32. The front-wheel rotation speed calculator71 and the rear-wheel rotation speed calculator 72 each obtain arotation angle based on a pulse signal, which is the output signal fromthe sensor, and differentiate the rotation angle by time elapsed so asto calculate the rotation speed.

The controller 70 includes a front-wheel displacement amount obtainer73. The front-wheel displacement amount obtainer 73 obtains afront-wheel displacement amount Lf based on the output signal from thefront-wheel relative position detector 281. The front-wheel displacementamount Lf is the amount of displacement of the upper-side end supportmember 270 of the front-wheel spring length adjustment unit 250 relativeto the base member 260. The controller 70 also includes a rear-wheeldisplacement amount obtainer 74. The rear-wheel displacement amountobtainer 74 obtains a rear-wheel displacement amount Lr based on theoutput signal from the rear-wheel relative position detector 282. Therear-wheel displacement amount Lr is the amount of displacement of theupper-side end support member 254 of the rear-wheel spring lengthadjustment unit 252 relative to the base member 253. The front-wheeldisplacement amount obtainer 73 obtains the front-wheel displacementamount Lf based on a correlation between the impedance of the coil andthe front-wheel displacement amount Lf. The rear-wheel displacementamount obtainer 74 obtains the rear-wheel displacement amount Lr basedon a correlation between the impedance of the coil and the rear-wheeldisplacement amount Lr. The correlations are stored in the ROM inadvance.

The controller 70 also includes a vehicle speed obtainer 76 to acquire avehicle speed Vv, which is a traveling speed of the motorcycle 1, basedon the rotation speed of the front wheel 2 calculated by the front-wheelrotation speed calculator 71 and/or based on the rotation speed of therear wheel 3 calculated by the rear-wheel rotation speed calculator 72.The vehicle speed obtainer 76 uses the front-wheel rotation speed Rf orthe rear-wheel rotation speed Rr to calculate a traveling speed of thefront wheel 2 or the rear wheel 3 so as to acquire the vehicle speed Vv.The traveling speed of the front wheel 2 is calculated using thefront-wheel rotation speed Rf and an outer diameter of the tire of thefront wheel 2. A traveling speed of the rear wheel 3 is calculated usingthe rear-wheel rotation speed Rr and an outer diameter of the tire ofthe rear wheel 3. When the motorcycle 1 is traveling in a normal state,it can be construed that the vehicle speed Vv is equal to the travelingspeed of the front wheel 2 and/or the traveling speed of the rear wheel3. Alternatively, the vehicle speed obtainer 76 may use an average valueof the front-wheel rotation speed Rf and the rear-wheel rotation speedRr to calculate an average traveling speed of the front wheel 2 and therear wheel 3 so as to acquire the vehicle speed Vv. It is noted that thefront-wheel rotation speed calculator 71, the rear-wheel rotation speedcalculator 72, and the vehicle speed obtainer 76 are an example of thevehicle speed obtainer to obtain the vehicle speed Vv.

The controller 70 also includes a malfunction detector 75, which is anexample of the malfunction detector to detect a failure to obtain anaccurate value of the vehicle speed Vv. The malfunction detector 75outputs the vehicle speed Vv obtained by the vehicle speed obtainer 76to a passage switch unit controller 77, described later, and also holdsthe vehicle speed Vv. In a normal state in which the malfunctiondetector 75 detects no failure to obtain the accurate vehicle speed Vv,the malfunction detector 75 outputs the vehicle speed Vv obtained by thevehicle speed obtainer 76 to the passage switch unit controller 77 as itis. When the malfunction detector 75 detects the failure to obtain theaccurate vehicle speed Vv, the malfunction detector 75 outputs a vehiclespeed Vv obtained by the vehicle speed obtainer 76 before occurrence ofthe failure to the passage switch unit controller 77.

The malfunction detector 75 will be described in detail later.

The controller 70 also includes the passage switch unit controller 77 tocontrol the switch states of the front-wheel passage switch unit 300 andthe switch states of the rear-wheel passage switch unit 302 based on thevehicle speed Vv obtained by the vehicle speed obtainer 76. The passageswitch unit controller 77 will be described in detail later.

The front-wheel rotation speed calculator 71, the rear-wheel rotationspeed calculator 72, the front-wheel displacement amount obtainer 73,the rear-wheel displacement amount obtainer 74, the malfunction detector75, the vehicle speed obtainer 76, and the passage switch unitcontroller 77 are implemented by the CPU executing software stored instorage areas of, for example, the ROM.

The passage switch unit controller 77 of the controller 70 will now bedescribed in detail.

FIG. 13 is a block diagram of the passage switch unit controller 77.

The passage switch unit controller 77 includes a target displacementamount determiner 770. The target displacement amount determiner 770includes a front-wheel target displacement amount determiner 771 and arear-wheel target displacement amount determiner 772. The front-wheeltarget displacement amount determiner 771 determines a front-wheeltarget displacement amount, which is a target value of the front-wheeldisplacement amount Lf. The rear-wheel target displacement amountdeterminer 772 determines a rear-wheel target displacement amount, whichis a target value of the rear-wheel displacement amount Lr. The passageswitch unit controller 77 also includes a target current determiner 710and a control section 720. The target current determiner 710 determinestarget currents to be supplied to the front-wheel solenoid 310 of thefront-wheel passage switch unit 300 and the rear-wheel solenoid (notillustrated) of the rear-wheel passage switch unit 302. The controlsection 720 performs control such as feedback control based on thetarget currents determined by the target current determiner 710. It isnoted that the passage switch unit controller 77 is an example of thevehicle height controller to control the vehicle height based on thevehicle speed Vv.

The target displacement amount determiner 770 determines a targetdisplacement amount based on the vehicle speed Vv obtained by thevehicle speed obtainer 76 and based on which control position a vehicleheight adjustment switch (not illustrated) of the motorcycle 1 occupies.The vehicle height adjustment switch is what is called a dial switch.The rider of the motorcycle 1 turns the dial of the switch to selectbetween “Low”, “Medium”, and “High”. The vehicle height adjustmentswitch is disposed in the vicinity of the speedometer, for example.

After the motorcycle 1 starts traveling, when the vehicle speed Vvobtained by the vehicle speed obtainer 76 is lower than a predeterminedupward vehicle speed Vu, the target displacement amount determiner 770determines the target displacement amount as zero. When the vehiclespeed Vv changes from the value lower than the upward vehicle speed Vuto a value equal to or higher than the upward vehicle speed Vu, thetarget displacement amount determiner 770 determines the targetdisplacement amount at a predetermined value in accordance with thecontrol position of the vehicle height adjustment switch. Morespecifically, when the vehicle speed Vv changes from the value lowerthan the upward vehicle speed Vu to a value equal to or higher than theupward vehicle speed Vu, the front-wheel target displacement amountdeterminer 771 determines the front-wheel target displacement amount asa predetermined front-wheel target displacement amount Lf0 in accordancewith the control position of the vehicle height adjustment switch. Whenthe vehicle speed Vv changes from the value lower than the upwardvehicle speed Vu to a value equal to or higher than the upward vehiclespeed Vu, the rear-wheel target displacement amount determiner 772determines the rear-wheel target displacement amount as a predeterminedrear-wheel target displacement amount Lr0 in accordance with the controlposition of the vehicle height adjustment switch. Then, while thevehicle speed Vv obtained by the vehicle speed obtainer 76 is equal toor higher than the upward vehicle speed Vu, the front-wheel targetdisplacement amount determiner 771 determines the front-wheel targetdisplacement amount as the predetermined front-wheel target displacementamount Lf0, and the rear-wheel target displacement amount determiner 772determines the rear-wheel target displacement amount as thepredetermined rear-wheel target displacement amount Lr0. The ROM stores,in advance, relationships of the control positions of the vehicle heightadjustment switch, the predetermined front-wheel target displacementamount Lf0 that accords with the control position, and the predeterminedrear-wheel target displacement amount Lr0 that accords with the controlposition. The vehicle height of the motorcycle 1 is determined inaccordance with the front-wheel displacement amount Lf and therear-wheel displacement amount Lr. In a non-limiting embodiment, atarget vehicle height, which is a target value of the vehicle height ofthe motorcycle 1, is determined in accordance with the control positionof the vehicle height adjustment switch. The predetermined front-wheeltarget displacement amount Lf0 and the predetermined rear-wheel targetdisplacement amount Lr0 in accordance with the target vehicle height aredetermined in advance and stored in the ROM.

When the vehicle speed Vv of the motorcycle 1 changes from a value equalto or higher than the upward vehicle speed Vu to a value equal to orlower than a predetermined downward vehicle speed Vd, the targetdisplacement amount determiner 770 determines the target displacementamount as zero. That is, the front-wheel target displacement amountdeterminer 771 and the rear-wheel target displacement amount determiner772 respectively determine the front-wheel target displacement amountand the rear-wheel target displacement amount as zero. In a non-limitingexample, the upward vehicle speed Vu is 7 km/h, and the downward vehiclespeed Vd is 5 km/h.

The target current determiner 710 includes a front-wheel target currentdeterminer 711 and a rear-wheel target current determiner 712. Based onthe front-wheel target displacement amount determined by the front-wheeltarget displacement amount determiner 771, the front-wheel targetcurrent determiner 711 determines a front-wheel target current, which isa target current of the front-wheel solenoid 310 of the front-wheelpassage switch unit 300. Based on the rear-wheel target displacementamount determined by the rear-wheel target displacement amountdeterminer 772, the rear-wheel target current determiner 712 determinesa rear-wheel target current, which is a target current of the rear-wheelsolenoid of the rear-wheel passage switch unit 302.

In a non-limiting embodiment, a map indicating correspondence betweenthe front-wheel target displacement amount and the front-wheel targetcurrent is prepared based on empirical rules and stored in the ROM inadvance. The front-wheel target current determiner 711 substitutes thefront-wheel target displacement amount determined by the front-wheeltarget displacement amount determiner 771 into the map to determine thefront-wheel target current.

In a non-limiting embodiment, a map indicating correspondence betweenthe rear-wheel target displacement amount and the rear-wheel targetcurrent is prepared based on empirical rules and stored in the ROM inadvance. The rear-wheel target current determiner 712 substitutes therear-wheel target displacement amount determined by the rear-wheeltarget displacement amount determiner 772 into the map to determine therear-wheel target current.

In the determination of the front-wheel target current based on thefront-wheel target displacement amount determined by the front-wheeltarget displacement amount determiner 771, the front-wheel targetcurrent determiner 711 may perform feedback control based on an errorbetween the front-wheel target displacement amount determined by thefront-wheel target displacement amount determiner 771 and thefront-wheel displacement amount Lf obtained by the front-wheeldisplacement amount obtainer 73 so as to determine the front-wheeltarget current. Similarly, in the determination of the rear-wheel targetcurrent based on the rear-wheel target displacement amount determined bythe rear-wheel target displacement amount determiner 772, the rear-wheeltarget current determiner 712 may perform feedback control based on anerror between the rear-wheel target displacement amount determined bythe rear-wheel target displacement amount determiner 772 and therear-wheel displacement amount Lr obtained by the rear-wheeldisplacement amount obtainer 74 so as to determine the rear-wheel targetcurrent.

The control section 720 includes the front-wheel solenoid driver 733, afront-wheel operation controller 730, and a front-wheel current detector734. The front-wheel solenoid driver 733 drives the front-wheel solenoid310 of the front-wheel passage switch unit 300. The front-wheeloperation controller 730 controls operation of the front-wheel solenoiddriver 733. The front-wheel current detector 734 detects the currentflowing to the front-wheel solenoid 310. The control section 720 alsoincludes a rear-wheel solenoid driver 743, a rear-wheel operationcontroller 740, and a rear-wheel current detector 744. The rear-wheelsolenoid driver 743 drives the rear-wheel solenoid. The rear-wheeloperation controller 740 controls operation of the rear-wheel solenoiddriver 743. The rear-wheel current detector 744 detects the currentflowing to the rear-wheel solenoid. It is noted that the front-wheelsolenoid driver 733 and the rear-wheel solenoid driver 743 are examplesof the actuator drivers to drive the actuators.

The front-wheel operation controller 730 includes a front-wheel feedback(F/B) controller 731 and a front-wheel PWM controller 732. Thefront-wheel feedback controller 731 performs feedback control based onan error between the front-wheel target current determined by thefront-wheel target current determiner 711 and a current detected by thefront-wheel current detector 734 (front-wheel detection current). Thefront-wheel PWM controller 732 performs PWM control of the front-wheelsolenoid 310.

The rear-wheel operation controller 740 includes a rear-wheel feedback(F/B) controller 741 and a rear-wheel PWM controller 742. The rear-wheelfeedback controller 741 performs feedback control based on an errorbetween the rear-wheel target current determined by the rear-wheeltarget current determiner 712 and a current detected by the rear-wheelcurrent detector 744 (rear-wheel detection current). The rear-wheel PWMcontroller 742 performs PWM control of the rear-wheel solenoid.

The front-wheel feedback controller 731 calculates an error between thefront-wheel target current and the front-wheel detection currentdetected by the front-wheel current detector 734, and performs feedbackprocessing to make the error zero. The rear-wheel feedback controller741 calculates an error between the rear-wheel target current and therear-wheel detection current detected by the rear-wheel current detector744, and performs feedback processing to make the error zero. In anon-limiting embodiment, the front-wheel feedback controller 731subjects the error between the front-wheel target current and thefront-wheel detection current to proportional processing using aproportional element and to integral processing using an integralelement, and adds these values together using an adder. The rear-wheelfeedback controller 741 subjects the error between the rear-wheel targetcurrent and the rear-wheel detection current to proportional processingusing a proportional element and to integral processing using anintegral element, and adds these values together using an adder. Inanother non-limiting embodiment, the front-wheel feedback controller 731subjects the error between the target current and the detection currentto proportional processing using a proportional element, to integralprocessing using an integral element, and to differential processingusing a differential element, and adds these values together using anadder. The rear-wheel feedback controller 741 subjects the error betweenthe target current and the detection current to proportional processingusing a proportional element, to integral processing using an integralelement, and to differential processing using a differential element,and adds these values together using an adder.

The front-wheel PWM controller 732 changes a duty ratio (=t/T×100(%)) ofa pulse width (t) in a predetermined cycle (T), and performs PWM controlof an opening (voltage applied to the coil 311 of the front-wheelsolenoid 310) of the front-wheel solenoid 310. When the PWM control isperformed, the voltage is applied to the coil 311 of the front-wheelsolenoid 310 in a form of a pulse that accords with the duty ratio.Here, due to the impedance of the coil 311, the current flowing to thecoil 311 of the front-wheel solenoid 310 cannot change to follow thevoltage applied in the form of the pulse but is output in a weakenedform, and the current flowing in the coil 311 of the front-wheelsolenoid 310 is increased and decreased in proportion to the duty ratio.In a non-limiting embodiment, when the front-wheel target current iszero, the front-wheel PWM controller 732 sets the duty ratio at zero.When the front-wheel target current is at its maximum, the front-wheelPWM controller 732 sets the duty ratio at 100%. In a non-limitingembodiment, when the duty ratio is set at 100%, a current of 3.2 A iscontrolled to flow to the coil 311 of the front-wheel solenoid 310. Whenthe duty ratio is set at 50%, a current of 1.6 A is controlled to flowto the coil 311 of the front-wheel solenoid 310.

Similarly, the rear-wheel PWM controller 742 changes the duty ratio andperforms PWM control of an opening (voltage applied to the coil of therear-wheel solenoid) of the rear-wheel solenoid. When the PWM control isperformed, the voltage is applied to the coil of the rear-wheel solenoidin a form of a pulse that accords with the duty ratio, and the currentflowing in the coil of the rear-wheel solenoid is increased anddecreased in proportion to the duty ratio. In a non-limiting embodiment,when the rear-wheel target current is zero, the rear-wheel PWMcontroller 742 sets the duty ratio at zero. When the rear-wheel targetcurrent is at its maximum, the rear-wheel PWM controller 742 sets theduty ratio at 100%. In a non-limiting embodiment, when the duty ratio isset at 100%, a current of 3.2 A is controlled to flow to the coil of therear-wheel solenoid. When the duty ratio is set at 50%, a current of 1.6A is controlled to flow to the coil of the rear-wheel solenoid.

The front-wheel solenoid driver 733 includes, for example, a transistor(FET). The transistor is a switching element connected between apositive electrode line of the power source and the coil 311 of thefront-wheel solenoid 310. The front-wheel solenoid driver 733 drives agate of this transistor to switch the transistor so as to control driveof the front-wheel solenoid 310. The rear-wheel solenoid driver 743includes, for example, a transistor connected between the positiveelectrode line of the power source and the coil of the rear-wheelsolenoid. The rear-wheel solenoid driver 743 drives a gate of thistransistor to switch the transistor so as to control drive of therear-wheel solenoid.

From voltage across terminals of a shunt resistor connected to thefront-wheel solenoid driver 733, the front-wheel current detector 734detects a value of the current flowing to the front-wheel solenoid 310.From voltage across terminals of a shunt resistor connected to therear-wheel solenoid driver 743, the rear-wheel current detector 744detects a value of the current flowing to the rear-wheel solenoid.

In the motorcycle 1 of the above-described configuration, the passageswitch unit controller 77 of the controller 70 determines the targetcurrent based on the target vehicle height in accordance with thecontrol position of the vehicle height adjustment switch, and performsPWM control to cause an actual current supplied to the front-wheelsolenoid 310 and the rear-wheel solenoid to be the target currentdetermined. That is, the front-wheel PWM controller 732 and therear-wheel PWM controller 742 of the passage switch unit controller 77change the duty ratios to control power supplied to the coil 311 of thefront-wheel solenoid 310 and the coil of the rear-wheel solenoid so asto control the front-wheel solenoid 310 and the rear-wheel solenoid intodesired openings.

When the failure of the vehicle speed obtainer 76 to obtain the accuratevehicle speed Vv occurs, the controller 70 of the above-describedconfiguration cannot appropriately adjust the vehicle height.

For example, when the vehicle speed obtainer 76 erroneously recognizesthat the vehicle speed Vv is zero although the motorcycle 1 istraveling, the target displacement amount determiner 770 determines thatthe target displacement amount is zero. In this case, to decrease thefront-wheel displacement amount Lf, the front-wheel target currentdeterminer 711 determines that the front-wheel target current is thedecreasing current (current equal to or higher than the second referencecurrent) to decrease the vehicle height. Similarly, the rear-wheeltarget current determiner 712 determines that the rear-wheel targetcurrent is the decreasing current to decrease the rear-wheeldisplacement amount Lr.

FIG. 14A is a time chart illustrating malfunction when the failure toobtain the accurate vehicle speed Vv occurs.

In the example illustrated in FIG. 14A, to maintain the vehicle heightafter increasing the vehicle height, the target current is set to be themaintenance current (current equal to or higher than zero and less thanthe first reference current). When the currents supplied to thefront-wheel solenoid 310 and the rear-wheel solenoid are controlled tobe the target current, the failure to obtain the accurate vehicle speedVv occurs.

As the failure to obtain the accurate vehicle speed Vv, a case can beconsidered in which the controller 70 cannot accurately obtain outputsignals from the front-wheel rotation detection sensor 31 and therear-wheel rotation detection sensor 32 due to the connector coming off,break, and communication failure of CAN (Controller Area Network)signals, for example. When the output signals from the front-wheelrotation detection sensor 31 and the rear-wheel rotation detectionsensor 32 cannot be obtained, the vehicle speed obtainer 76 mayerroneously recognize that the vehicle speed Vv is zero, for example.Another case can be considered in which the front-wheel rotationdetection sensor 31 and the rear-wheel rotation detection sensor 32themselves become out of order, and although the wheels are rotating,the sensors output a value indicating zero, for example. When suchmalfunction of the sensors themselves occurs, the vehicle speed obtainer76 may also erroneously recognize that the vehicle speed Vv is zero.This is equivalent to the failure to obtain the accurate vehicle speedVv.

When the failure to obtain the accurate vehicle speed Vv occurs, thevehicle speed obtainer 76 may erroneously recognize that the vehiclespeed Vv is zero, for example. In this case, the front-wheel targetcurrent determiner 711 continues to determine that the front-wheeltarget current is the decreasing current. The rear-wheel target currentdeterminer 712 continues to determine that the rear-wheel target currentis the decreasing current. As a result, even if the vehicle speed Vv ofthe motorcycle 1 is equal to or higher than the upward vehicle speed Vu,the front-wheel displacement amount Lf and the rear-wheel displacementamount Lr decrease, and the vehicle height decreases. When the vehicleheight unexpectedly decreases during travel at a speed equal to orhigher than the upward vehicle speed Vu, it becomes difficult for therider to incline the body of the motorcycle 1, for example, which makesit difficult to secure a sufficiently large bank angle.

As the failure to obtain the accurate vehicle speed Vv, a case can beconsidered in which although the actual vehicle speed Vv is equal to orhigher than the upward vehicle speed Vu, the vehicle speed obtainer 76erroneously recognizes that the actual vehicle speed Vv is equal to orlower than the downward vehicle speed Vd. Preferably, a case in whichthe vehicle speed obtainer 76 erroneously recognizes that the vehiclespeed Vv is 1 km/h or more deviated from the actual vehicle speed Vv canbe regarded as the failure to obtain the accurate vehicle speed Vv.

It can be also considered that when the target current is set to be theincreasing current (current equal to or higher than the first referencecurrent and less than the second reference current) to increase thevehicle height, for example, and when the currents supplied to thefront-wheel solenoid 310 and the rear-wheel solenoid are controlled tobe the target current, the failure to obtain the accurate vehicle speedVv occurs. In this manner, when the failure to obtain the accuratevehicle speed Vv occurs with the target current being set at theincreasing current, the front-wheel target current determiner 711continues to determine that the front-wheel target current is thedecreasing current. Also, the rear-wheel target current determiner 712continues to determine that the rear-wheel target current is thedecreasing current. As a result, in the middle of an increase in thevehicle height of the motorcycle 1, the front-wheel displacement amountLf and the rear-wheel displacement amount Lr decrease, and the vehicleheight decreases. When the vehicle height unexpectedly decreases duringtravel at a speed equal to or higher than the upward vehicle speed Vu,it becomes difficult for the rider to incline the body of the motorcycle1, for example, which makes it difficult to secure a sufficiently largebank angle.

Details of Malfunction Detector 75

In view of the above-described circumstances, the malfunction detector75 according to this embodiment detects the failure of the vehicle speedobtainer 76 to obtain the accurate vehicle speed Vv. Detecting thefailure, the malfunction detector 75 outputs to the front-wheel passageswitch unit 300 and the rear-wheel passage switch unit 302 a vehiclespeed Vv obtained by the vehicle speed obtainer 76 before occurrence ofthe failure.

A rotation speed is calculated based on an output signal (detectionvalue) from one of the front-wheel rotation detection sensor 31 and therear-wheel rotation detection sensor 32. The malfunction detector 75first makes a determination as to whether the rotation speed changesfrom a speed equal to or higher than a predetermined speed Va to a speedequal to or lower than a halt determination speed Vb in one sample cycleto obtain the output signal from the one of the front-wheel rotationdetection sensor 31 and the rear-wheel rotation detection sensor 32. Inother words, the malfunction detector 75 compares a rotation speedcalculated based on an output signal previously obtained from each ofthe front-wheel rotation detection sensor 31 and the rear-wheel rotationdetection sensor 32 with a rotation speed calculated based on an outputsignal obtained anew. Then, the malfunction detector 75 makes adetermination as to whether the rotation speed changes from a speedequal to or higher than the predetermined speed Va to a speed equal toor lower than the halt determination speed Vb.

It is noted that the predetermined speed Va is an example of the firstreference speed and depends on the specifications of the motorcycle 1.In a non-limiting example, the predetermined speed Va is a rotationspeed to make the vehicle speed Vv 10 km/h. The halt determination speedVb, which is an example of the second reference speed, is lower than thespeed Va. In a non-limiting example, the halt determination speed Vb isa rotation speed to make the vehicle speed Vv 0 km/h to 3 km/h. In anon-limiting example, one sample cycle, which is an example of thereference period of time, is 10 msec.

When the rotation speed, which is calculated based on the output signalfrom the one of the front-wheel rotation detection sensor 31 and therear-wheel rotation detection sensor 32, changes from the speed equal toor higher than the predetermined speed Va to the speed equal to or lowerthan the halt determination speed Vb in one sample cycle, themalfunction detector 75 further makes a determination as to a rotationspeed based on an output signal (detection value) from the other of thefront-wheel rotation detection sensor 31 and the rear-wheel rotationdetection sensor 32. More specifically, the malfunction detector 75makes a determination as to whether the rotation speed, which is basedon the output signal from the other of the front-wheel rotationdetection sensor 31 and the rear-wheel rotation detection sensor 32,changes from a speed equal to or higher than the predetermined speed Vato a speed equal to or lower than the halt determination speed Vb in onesample cycle to obtain the output signal from the other of thefront-wheel rotation detection sensor 31 and the rear-wheel rotationdetection sensor 32. In other words, the malfunction detector 75compares a rotation speed calculated based on an output signalpreviously obtained from the other of the front-wheel rotation detectionsensor 31 and the rear-wheel rotation detection sensor 32 with arotation speed calculated based on an output signal obtained anew. Then,the malfunction detector 75 makes a determination as to whether therotation speed changes from a speed equal to or higher than thepredetermined speed Va to a speed equal to or lower than the haltdetermination speed Vb.

When the rotation speed, which is calculated based on the output signalfrom the other of the front-wheel rotation detection sensor 31 and therear-wheel rotation detection sensor 32, changes from the speed equal toor higher than the predetermined speed Va to the speed equal to or lowerthan the halt determination speed Vb in one sample cycle, themalfunction detector 75 makes a determination as to whether a period oftime in which the rotation speed of the front wheel 2 detected by thefront-wheel rotation detection sensor 31 and the rotation speed of therear wheel 3 detected by the rear-wheel rotation detection sensor 32 areboth equal to or lower than the speed Vb becomes a first predeterminedperiod of time t1 or longer. When this period of time becomes the firstpredetermined period of time t1 or longer, the malfunction detector 75determines that the failure to obtain the accurate vehicle speed Vv hasoccurred. At this time, the malfunction detector 75 presumes that thefailure to obtain the accurate vehicle speed Vv has occurred because thevehicle speed obtainer 76 (or the front-wheel rotation speed calculator71 and the rear-wheel rotation speed calculator 72) has become unable toobtain detection values detected by the front-wheel rotation detectionsensor 31 and the rear-wheel rotation detection sensor 32 or because thefront-wheel rotation detection sensor 31 and the rear-wheel rotationdetection sensor 32 have become unable to detect the detection values.

When determining that the failure to obtain the accurate vehicle speedVv has occurred, the malfunction detector 75 lights the warning lamp andoutputs to the passage switch unit controller 77 the vehicle speed Vvobtained by the vehicle speed obtainer 76 before occurrence of thefailure. In other words, the malfunction detector 75 outputs to thepassage switch unit controller 77 the vehicle speed Vv obtained based onthe rotation speeds (the rotation speed of the front wheel 2 and therotation speed of the rear wheel 3) calculated in one sample cyclebefore occurrence of the failure.

As a result, the vehicle height is controlled based on the vehicle speedVv obtained by the vehicle speed obtainer 76 before occurrence of thefailure. That is, the vehicle height decreases in the firstpredetermined period of time t1 after occurrence of the failure. Whenthe malfunction detector 75 detects the failure, however, the vehicleheight is controlled based on the vehicle speed Vv obtained by thevehicle speed obtainer 76 before occurrence of the failure.Consequently, when the vehicle speed Vv is equal to or higher than theupward vehicle speed Vu before occurrence of the failure, thefront-wheel target displacement amount determiner 771 determines thatthe front-wheel target displacement amount is the predeterminedfront-wheel target displacement amount Lf0. The rear-wheel targetdisplacement amount determiner 772 determines that the rear-wheel targetdisplacement amount is the predetermined rear-wheel target displacementamount Lr0. Then, the vehicle height increases to the target vehicleheight. That is, when the failure to obtain the accurate vehicle speedVv occurs, a difference between the actual front-wheel displacementamount Lf and the predetermined front-wheel target displacement amountLf0 and a difference between the actual rear-wheel displacement amountLr and the predetermined rear-wheel target displacement amount Lr0 startto increase. Then, after the first predetermined period of time t1elapses, the front-wheel displacement amount Lf and the rear-wheeldisplacement amount Lr are respectively controlled to be thepredetermined front-wheel target displacement amount Lf0 and thepredetermined rear-wheel target displacement amount Lr0, which aretarget displacement amounts before the differences start to increase.

FIG. 14B is a time chart illustrating control details of the malfunctiondetector 75 according to this embodiment. In the example illustrated inFIG. 14B, which is similar to the example illustrated in FIG. 14A, thefailure occurs when the vehicle height is increased and maintained.

The malfunction detector 75 makes a determination as to whether arotation speed based on an output signal from one of the front-wheelrotation detection sensor 31 and the rear-wheel rotation detectionsensor 32 changes from a speed equal to or higher than the speed Va to aspeed equal to or lower than the speed Vb in one sample cycle to obtainthe output signal from the one of the front-wheel rotation detectionsensor 31 and the rear-wheel rotation detection sensor 32. Further, themalfunction detector 75 makes a determination as to whether a rotationspeed based on an output signal from the other of the front-wheelrotation detection sensor 31 and the rear-wheel rotation detectionsensor 32 changes from a speed equal to or higher than the speed Va to aspeed equal to or lower than the speed Vb in one sample cycle to obtainthe output signal from the other of the front-wheel rotation detectionsensor 31 and the rear-wheel rotation detection sensor 32.

When a period of time in which the rotation speed based on the outputsignal from the front-wheel rotation detection sensor 31 and therotation speed based on the output signal from the rear-wheel rotationdetection sensor 32 are equal to or lower than the speed Vb becomes thefirst predetermined period of time t1 or longer, the malfunctiondetector 75 determines that the failure to obtain the accurate vehiclespeed Vv has occurred. Then, the malfunction detector 75 outputs to thepassage switch unit controller 77 a vehicle speed Vv obtained by thevehicle speed obtainer 76 before occurrence of the failure. As a result,although occurrence of the failure causes the vehicle height todecrease, the malfunction detector 75 detects the failure to control thevehicle height based on the vehicle speed Vv obtained by the vehiclespeed obtainer 76 before occurrence of the failure. Then, the vehicleheight increases to be the target vehicle height.

Next, using a flowchart, a procedure for the control processingperformed by the malfunction detector 75 will be described.

FIG. 15 is the flowchart of the procedure for the control processingperformed by the malfunction detector 75.

In a non-limiting example, the malfunction detector 75 performs thecontrol processing in every predetermined cycle (1 msec, for example)repeatedly.

First, the malfunction detector 75 makes a determination as to whether aflag is ON in one of the front-wheel rotation detection sensor 31 andthe rear-wheel rotation detection sensor 32 (S101). This is theprocessing for making a determination as to whether the flag set in theRAM at S104 or S106, described later, is ON. When the flag is ON in oneof the front-wheel rotation detection sensor 31 and the rear-wheelrotation detection sensor 32 (Yes at S101), the malfunction detector 75makes a determination as to whether a flag is ON in the other of thefront-wheel rotation detection sensor 31 and the rear-wheel rotationdetection sensor 32 (S102). When the flag is ON in the other of thefront-wheel rotation detection sensor 31 and the rear-wheel rotationdetection sensor 32 (Yes at S102), the processing proceeds to S109,described later.

When at S101 the flag is not ON in both of the front-wheel rotationdetection sensor 31 and the rear-wheel rotation detection sensor 32 (Noat S101), the malfunction detector 75 makes a determination as towhether a rotation speed based on an output signal from one of thefront-wheel rotation detection sensor 31 and the rear-wheel rotationdetection sensor 32 (namely, a rotation speed of one of the front wheel2 and the rear wheel 3) changes from a speed equal to or higher than thespeed Va to a speed equal to or lower than the speed Vb in one samplecycle to obtain the output signal from the one of the front-wheelrotation detection sensor 31 and the rear-wheel rotation detectionsensor 32 (S103). In a non-limiting embodiment, concerning thefront-wheel rotation detection sensor 31, the malfunction detector 75makes a determination as to whether a rotation speed based on an outputsignal from the front-wheel rotation detection sensor 31 changes from aspeed equal to or higher than the speed Va to a speed equal to or lowerthan the speed Vb in one sample cycle to obtain the output signal fromthe front-wheel rotation detection sensor 31. In another non-limitingembodiment, concerning the rear-wheel rotation detection sensor 32, themalfunction detector 75 makes a determination as to whether a rotationspeed based on an output signal from the rear-wheel rotation detectionsensor 32 changes from a speed equal to or higher than the speed Va to aspeed equal to or lower than the speed Vb in one sample cycle to obtainthe output signal from the rear-wheel rotation detection sensor 32.

When at S103 the rotation speeds based on the output signals from bothof the front-wheel rotation detection sensor 31 and the rear-wheelrotation detection sensor 32 do not change from the speed equal to orhigher than the speed Va to the speed equal to or lower than the speedVb (No at S103), the malfunction detector 75 ends performance of thiscontrol processing.

When the rotation speed based on the output signal from the one of thefront-wheel rotation detection sensor 31 and the rear-wheel rotationdetection sensor 32 changes from the speed equal to or higher than thespeed Va to the speed equal to or lower than the speed Vb (Yes at S103),the malfunction detector 75 sets the flag of the one of the front-wheelrotation detection sensor 31 and the rear-wheel rotation detectionsensor 32 to be ON in the RAM (S104).

After S104 or when the determination at S102 is negative (No), themalfunction detector 75 makes a determination as to whether a rotationspeed based on an output signal from the other of the front-wheelrotation detection sensor 31 and the rear-wheel rotation detectionsensor 32 changes from a speed equal to or higher than the speed Va to aspeed equal to or lower than the speed Vb in one sample cycle to obtainthe output signal from the other of the front-wheel rotation detectionsensor 31 and the rear-wheel rotation detection sensor 32 (S105). In anon-limiting embodiment, when at S101 the flag of the front-wheelrotation detection sensor 31 is ON, and the flag of the rear-wheelrotation detection sensor 32 is OFF, the malfunction detector 75 makes adetermination as to whether the rotation speed of the rear wheel 3changes from a speed equal to or higher than the speed Va to a speedequal to or lower than the speed Vb at S105. In another non-limitingembodiment, when at S103 the rotation speed of the front wheel 2 changesfrom the speed equal to or higher than the speed Va to the speed equalto or lower than the speed Vb, the malfunction detector 75 makes adetermination as to whether the rotation speed of the rear wheel 3changes from a speed equal to or higher than the speed Va to a speedequal to or lower than the speed Vb at S105.

When the rotation speed based on the output signal from the other of thefront-wheel rotation detection sensor 31 and the rear-wheel rotationdetection sensor 32 (namely, the rotation speed of the other of thefront wheel 2 and the rear wheel 3) changes from the speed equal to orhigher than the speed Va to the speed equal to or lower than the speedVb (Yes at S105), the malfunction detector 75 sets the flag of the otherof the front-wheel rotation detection sensor 31 and the rear-wheelrotation detection sensor 32 to be ON in the RAM (S106). Meanwhile, whenthe rotation speed based on the output signal from the other of thefront-wheel rotation detection sensor 31 and the rear-wheel rotationdetection sensor 32 does not change from the speed equal to or higherthan the speed Va to the speed equal to or lower than the speed Vb (Noat S105), the processing proceeds to S107. At S107, concerning one ofthe front-wheel rotation detection sensor 31 and the rear-wheel rotationdetection sensor 32 the flag of which is ON, the malfunction detector 75makes a determination as to whether the sample cycle is repeated, andthe one of the front-wheel rotation detection sensor 31 and therear-wheel rotation detection sensor 32 the flag of which is ON outputsa new output signal (S107). When the one of the front-wheel rotationdetection sensor 31 and the rear-wheel rotation detection sensor 32 theflag of which is ON outputs the new output signal (Yes at S107), themalfunction detector 75 makes the flag of the one of the front-wheelrotation detection sensor 31 and the rear-wheel rotation detectionsensor 32 OFF (S108), and ends performance of this control processing.Meanwhile, when the one of the front-wheel rotation detection sensor 31and the rear-wheel rotation detection sensor 32 the flag of which is ONdoes not output a new output signal (No at S107), the malfunctiondetector 75 keeps the flag of the one of the front-wheel rotationdetection sensor 31 and the rear-wheel rotation detection sensor 32 ON,and ends performance of this control processing.

After S106 or when the determination at S102 is positive (Yes), themalfunction detector 75 increases the continuation counter (S109). Next,the malfunction detector 75 makes a determination as to whether thecontinuation counter is equal to or larger than a first reference valuedetermined in advance as a value equivalent to the first predeterminedperiod of time t1 (S110). This is the processing for making adetermination as to whether the period of time in which the rotationspeed of the front wheel 2 and the rotation speed of the rear wheel 3are both equal to or lower than the speed Vb is equal to or longer thanthe first predetermined period of time t1.

When the continuation counter is equal to or larger than the firstreference value (Yes at S110), the malfunction detector 75 determinesthat the failure of the vehicle speed obtainer 76 to obtain the accuratevehicle speed Vv has occurred. Then, the malfunction detector 75 lightsthe warning lamp, and outputs to the passage switch unit controller 77 avalue of the vehicle speed Vv obtained by the vehicle speed obtainer 76before occurrence of the failure (S111). Also, the malfunction detector75 resets the continuation counter and ends this control processing.

Meanwhile, when at S110 the continuation counter is less than the firstreference value (No at S110), the malfunction detector 75 makes adetermination as to whether both of the rotation speed based on theoutput signal from the front-wheel rotation detection sensor 31 and therotation speed based on the output signal from the rear-wheel rotationdetection sensor 32 continue to be equal to or lower than the speed Vb(S112). When both of the rotation speeds continue to be equal to orlower than the speed Vb (Yes at S112), the malfunction detector 75 endsperformance of this control processing. Meanwhile, when one of therotation speed based on the output signal from the front-wheel rotationdetection sensor 31 and the rotation speed based on the output signalfrom the rear-wheel rotation detection sensor 32 is higher than thespeed Vb (No at S112), the malfunction detector 75 makes the flags ofboth of the front-wheel rotation detection sensor 31 and the rear-wheelrotation detection sensor 32 OFF and resets the continuation counter(S113). Then, the malfunction detector 75 ends performance of thiscontrol processing.

It is noted that the first predetermined period of time t1 may bechanged in accordance with the vehicle speed Vv. In a non-limitingexample, the first predetermined period of time t1 is 80 msec when thevehicle speed Vv is equal to or higher than 40 km/h. As in this example,the first predetermined period of time t1 may be made shorter as thevehicle speed Vv is higher. The reason is that as the vehicle speed Vvis higher, it becomes more difficult to incline the body of themotorcycle 1 when the vehicle height unexpectedly decrease duringtravel.

The malfunction detector 75 of the above-described configuration detectsthe failure of the vehicle speed obtainer 76 to obtain the accuratevehicle speed Vv based on the change in the rotation speeds of thewheels based on the output signals from the front-wheel rotationdetection sensor 31 and the rear-wheel rotation detection sensor 32.When the failure is detected, the malfunction detector 75 holds thevalue of the vehicle speed Vv at a value of the vehicle speed Vv beforeoccurrence of the failure and outputs the value of the vehicle speed Vvto the passage switch unit controller 77. Thus, a decrease in thevehicle height is eliminated or minimized, and this prevents the vehicleheight from unexpectedly decreasing in spite of high-speed travel, forexample. This in turn prevents the unexpected decrease in the vehicleheight during the travel from making it difficult for the rider toincline the body of the motorcycle 1.

In the above-described embodiment, the malfunction detector 75 detectsthe failure based on the change in the rotation speed based on theoutput signal from the front-wheel rotation detection sensor 31 and thechange in the rotation speed based on the output signal from therear-wheel rotation detection sensor 32. This, however, should not beconstrued in a limiting sense. For example, the malfunction detector 75may detect the failure based on a change in the vehicle speed Vvobtained from the rotation speed of the front wheel 2 and a change inthe vehicle speed Vv obtained from the rotation speed of the rear wheel3.

In the above-described embodiment, when the malfunction detector 75determines that the failure has occurred, the vehicle speed Vv is heldat the value of the vehicle speed Vv obtained before occurrence of thefailure so as to control the vehicle height. This, however, should notbe construed in a limiting sense. When the malfunction detector 75determines that the failure has occurred, the malfunction detector 75may control, for example, to make the front-wheel passage switch unit300 and the rear-wheel passage switch unit 302 shift to the first switchstate. When the malfunction detector 75 controls to make the front-wheelpassage switch unit 300 shift to the first switch state, for example,the front-wheel target current is set at the maintenance current tomaintain the vehicle height.

Here, when the malfunction detector 75 detects the failure, instead ofsetting the front-wheel target current at the maintenance current, thepassage switch unit controller 77 may turn off (break) a front-wheelrelay (not illustrated). The front-wheel relay is connected to a currentpath between the front-wheel solenoid driver 733 and the front-wheelsolenoid 310 to turn on or off the current supplied from the front-wheelsolenoid driver 733 to the front-wheel solenoid 310. Similarly, when themalfunction detector 75 detects the failure, instead of setting therear-wheel target current at the maintenance current, the passage switchunit controller 77 may turn off (break) a rear-wheel relay (notillustrated). The rear-wheel relay is connected to a current pathbetween the rear-wheel solenoid driver 743 and the rear-wheel solenoidto turn on or off the current supplied from the rear-wheel solenoiddriver 743 to the rear-wheel solenoid.

FIG. 16 is a time chart illustrating other control details of themalfunction detector according to this embodiment. In the exampleillustrated in FIG. 16, when the malfunction detector 75 detects thefailure, the front-wheel relay and the rear-wheel relay are turned offto shut off the current supplied to the front-wheel solenoid 310 and thecurrent supplied to the rear-wheel solenoid. It is noted that similarlyto the examples illustrated in FIGS. 14A and 14B, the failure occurswhen the vehicle height is increased and maintained.

First, similarly to the example illustrated in FIG. 14B, the malfunctiondetector 75 makes a determination as to whether a rotation speed basedon an output signal from one of the front-wheel rotation detectionsensor 31 and the rear-wheel rotation detection sensor 32 changes from aspeed equal to or higher than the speed Va to a speed equal to or lowerthan the speed Vb in one sample cycle to obtain the output signal fromthe one of the front-wheel rotation detection sensor 31 and therear-wheel rotation detection sensor 32. Further, the malfunctiondetector 75 makes a determination as to whether a rotation speed basedon an output signal from the other of the front-wheel rotation detectionsensor 31 and the rear-wheel rotation detection sensor 32 changes from aspeed equal to or higher than the speed Va to a speed equal to or lowerthan the speed Vb in one sample cycle to obtain the output signal fromthe other of the front-wheel rotation detection sensor 31 and therear-wheel rotation detection sensor 32.

Then, when a period of time in which the rotation speed based on theoutput signal from the front-wheel rotation detection sensor 31 and therotation speed based on the output signal from the rear-wheel rotationdetection sensor 32 are equal to or lower than the speed Vb becomes thefirst predetermined period of time t1 or longer, the malfunctiondetector 75 determines that the failure to obtain the accurate vehiclespeed Vv has occurred. Here, in the example illustrated in FIG. 16, thefront-wheel relay and the rear-wheel relay are turned off, and thecurrent supplied to the front-wheel solenoid 310 and the currentsupplied to the rear-wheel solenoid are shut off. As a result, thefront-wheel passage switch unit 300 and the rear-wheel passage switchunit 302 shift to the first switch state to control to maintain thevehicle height. In other words, when the failure to obtain the accuratevehicle speed Vv occurs, a difference between the actual front-wheeldisplacement amount Lf and the predetermined front-wheel targetdisplacement amount Lf0 and a difference between the actual rear-wheeldisplacement amount Lr and the predetermined rear-wheel targetdisplacement amount Lr0 start to increase. Then, after the firstpredetermined period of time t1 elapses, the vehicle height iscontrolled to be maintained.

Each of the front-wheel passage switch unit 300 and the rear-wheelpassage switch unit 302 controls, as a single unit, three control modesin accordance with the amount of the current. The three control modesare: an increasing mode for increasing the vehicle height, a decreasingmode for decreasing the vehicle height, and a maintenance mode formaintaining the vehicle height. In the above-described embodiment, thecontrol performed by the malfunction detector 75 is applied to thefront-wheel passage switch unit 300 and the rear-wheel passage switchunit 302 to control the three control modes as a single unit.Application of the control performed by the malfunction detector 75,however, should not be limited to the unit to control the three controlmodes as a single unit. The control may be applied to a configuration inwhich the three control modes are implemented by two control valves(electromagnetic actuators).

In Japanese Examined Patent Publication No. 8-22680, with the vehicleheight adjustment device to control the height of the motorcycle basedon the speed of the motorcycle, a failure to obtain an accurate value ofthe speed of the motorcycle makes it difficult to adjust the height ofthe motorcycle. For example, when the failure to obtain the accuratevalue of the speed of the motorcycle occurs while the motorcycle istraveling at high speed, there is a possibility of a sudden decrease inthe height of the motorcycle in spite of the high-speed travel. When theheight of the motorcycle unexpectedly decreases during the travel, itbecomes difficult for the rider of the motorcycle to incline the body ofthe motorcycle and secure a sufficiently large bank angle. In view ofthis, it is important to detect the failure to obtain the accurate valueof the speed of the motorcycle.

In a non-limiting embodiment, the vehicle height adjustment device mayfurther include a plurality of rotation angle detectors disposed on therespective wheels and configured to detect rotation angles of theplurality of wheels. The vehicle speed obtainer may be configured toobtain the vehicle speed based on detection values obtained by theplurality of rotation angle detectors. The malfunction detector may beconfigured to determine that the failure has occurred when the vehiclespeed obtainer has become unable to obtain the detection values from theplurality of rotation angle detectors or when the plurality of rotationangle detectors have become unable to detect the detection values.

In a non-limiting embodiment, the malfunction detector may be configuredto detect the failure based on changes in speeds based on the respectivedetection values obtained from the plurality of rotation angledetectors.

In a non-limiting embodiment, the plurality of rotation angle detectorsmay include a first rotation angle detector and a second rotation angledetector. The malfunction detector may be configured to determine thatthe failure has occurred after a first speed based on a detection valuedetected by the first rotation angle detector decreases from a valueequal to or higher than a first reference speed to a value equal to orlower than a second reference speed in a reference period of time, andafter a second speed based on a detection value detected by the secondrotation angle detector decreases from a value equal to or higher thanthe first reference speed to a value equal to or lower than the secondreference speed in the reference period of time, and when a state inwhich both of the first speed and the second speed are equal to or lowerthan the second reference speed continues for a predetermined period oftime.

In a non-limiting embodiment, when the malfunction detector detects thefailure, the vehicle height controller may be configured to control thevehicle height based on a vehicle speed obtained by the vehicle speedobtainer before occurrence of the failure.

In a non-limiting embodiment, the changer may include an actuator driveninto operation when supplied with a current and configured to change therelative position. The vehicle height controller may include an actuatordriver and a relay. The actuator driver may be configured to drive theactuator. The relay may be configured to electrically connect theactuator driver with the actuator and disconnect the actuator driverfrom the actuator. The vehicle height controller may be configured tobreak the relay when the malfunction detector detects the failure.

The embodiments of the present disclosure make it possible to detect thefailure to obtain the accurate vehicle speed.

Obviously, numerous modifications and variations of the presentdisclosure are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, thepresent disclosure may be practiced otherwise than as specificallydescribed herein.

What is claimed is:
 1. A vehicle height adjustment device comprising: a changer configured to change a relative position of a body of a vehicle, which comprises a plurality of wheels, relative to an axle of each of the plurality of wheels of the vehicle; a vehicle speed obtainer configured to obtain a vehicle speed, which is a traveling speed of the vehicle; a vehicle height controller configured to control a vehicle height, which is a height of the body, based on the vehicle speed obtained by the vehicle speed obtainer; and a malfunction detector configured to detect a failure of the vehicle speed obtainer to obtain an accurate value of the vehicle speed.
 2. The vehicle height adjustment device according to claim 1, further comprising a plurality of rotation angle detectors disposed on the respective wheels and configured to detect rotation angles of the plurality of wheels, wherein the vehicle speed obtainer is configured to obtain the vehicle speed based on detection values obtained by the plurality of rotation angle detectors, and wherein the malfunction detector is configured to determine that the failure has occurred when the vehicle speed obtainer has become unable to obtain the detection values from the plurality of rotation angle detectors or when the plurality of rotation angle detectors have become unable to detect the detection values.
 3. The vehicle height adjustment device according to claim 2, wherein the malfunction detector is configured to detect the failure based on changes in speeds based on the respective detection values obtained from the plurality of rotation angle detectors.
 4. The vehicle height adjustment device according to claim 3, wherein the plurality of rotation angle detectors comprise a first rotation angle detector and a second rotation angle detector, and wherein the malfunction detector is configured to determine that the failure has occurred after a first speed based on a detection value detected by the first rotation angle detector decreases from a value equal to or higher than a first reference speed to a value equal to or lower than a second reference speed in a reference period of time, and after a second speed based on a detection value detected by the second rotation angle detector decreases from a value equal to or higher than the first reference speed to a value equal to or lower than the second reference speed in the reference period of time, and when a state in which both of the first speed and the second speed are equal to or lower than the second reference speed continues for a predetermined period of time.
 5. The vehicle height adjustment device according to claim 1, wherein when the malfunction detector detects the failure, the vehicle height controller is configured to control the vehicle height based on a vehicle speed obtained by the vehicle speed obtainer before occurrence of the failure.
 6. The vehicle height adjustment device according to claim 1, wherein the changer comprises an actuator drivable when supplied with a current and configured to change the relative position, wherein the vehicle height controller comprises: an actuator driver configured to drive the actuator; and a relay configured to electrically connect the actuator driver with the actuator and electrically disconnect the actuator driver from the actuator, and wherein the vehicle height controller is configured to break the relay when the malfunction detector detects the failure.
 7. A vehicle height adjustment device comprising: a changer configured to change a relative position of a body of a vehicle relative to an axle of a wheel of the vehicle; and a vehicle height controller configured to, when a vehicle speed, which is a traveling speed of the vehicle, is equal to or higher than a predetermined upward speed, control the changer to make the relative position a target relative position, and configured to, when a difference between the actual relative position and the target relative position starts to increase although the vehicle speed is equal to or higher than the upward speed, and after a predetermined period of time elapses after the difference starts to increase, control the changer to make the relative position the target relative position before the difference starts to increase.
 8. A vehicle height adjustment device comprising: a changer configured to change a relative position of a body of a vehicle relative to an axle of a wheel of the vehicle; and a vehicle height controller configured to, when a vehicle speed, which is a traveling speed of the vehicle, is equal to or higher than a predetermined upward speed, control the changer to make the relative position a target relative position, and configured to, when a difference between the actual relative position and the target relative position starts to increase although the vehicle speed is equal to or higher than the upward speed, and after a predetermined period of time elapses after the difference starts to increase, control the changer to maintain a vehicle height, which is a height of the body.
 9. The vehicle height adjustment device according to claim 2, wherein when the malfunction detector detects the failure, the vehicle height controller is configured to control the vehicle height based on a vehicle speed obtained by the vehicle speed obtainer before occurrence of the failure.
 10. The vehicle height adjustment device according to claim 3, wherein when the malfunction detector detects the failure, the vehicle height controller is configured to control the vehicle height based on a vehicle speed obtained by the vehicle speed obtainer before occurrence of the failure.
 11. The vehicle height adjustment device according to claim 4, wherein when the malfunction detector detects the failure, the vehicle height controller is configured to control the vehicle height based on a vehicle speed obtained by the vehicle speed obtainer before occurrence of the failure.
 12. The vehicle height adjustment device according to claim 2, wherein the changer comprises an actuator drivable when supplied with a current and configured to change the relative position, wherein the vehicle height controller comprises: an actuator driver configured to drive the actuator; and a relay configured to electrically connect the actuator driver with the actuator and electrically disconnect the actuator driver from the actuator, and wherein the vehicle height controller is configured to break the relay when the malfunction detector detects the failure.
 13. The vehicle height adjustment device according to claim 3, wherein the changer comprises an actuator drivable when supplied with a current and configured to change the relative position, wherein the vehicle height controller comprises: an actuator driver configured to drive the actuator; and a relay configured to electrically connect the actuator driver with the actuator and electrically disconnect the actuator driver from the actuator, and wherein the vehicle height controller is configured to break the relay when the malfunction detector detects the failure.
 14. The vehicle height adjustment device according to claim 4, wherein the changer comprises an actuator drivable when supplied with a current and configured to change the relative position, wherein the vehicle height controller comprises: an actuator driver configured to drive the actuator; and a relay configured to electrically connect the actuator driver with the actuator and electrically disconnect the actuator driver from the actuator, and wherein the vehicle height controller is configured to break the relay when the malfunction detector detects the failure. 